1
If the investigator gathers them, the data are —
💡 Hint:
One’s own purpose.
Explanation:
Primary.
Class 9 · Maths · Chapter 14 · बिहार बोर्ड (BSEB)CBSE · NCERT 2026-27
Statistics
Statistics
How to use this page:
1. Read — Activity 1 · Exercise 14.1 · Activity 2 · Exercise 14.2 · Activity 3 · histogram · frequency polygon · Exercise 14.3 · mean · median · mode · Exercise 14.4, diagram, worked example, board tip
2. Check — each lesson has its own questions; the number follows the lesson
3. Mastery ★ — all of that lesson correct. Redo the wrong ones
4. The memory figure shows a histogram of touching bars and a frequency polygon joined through the class marks.
This page follows the Bihar textbook. Ganita Manjari uses a different order. Progress stays in this browser.
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- 1 Data and Activity 1
- 2 A frequency table
- 3 Bar graphs and Activity 3
- 4 Histogram and unequal widths
- 5 Frequency polygon and Exercise 14.3
- 6 The mean
- 7 Median, mode, and Exercise 14.4
- Chapter winner — every lesson at mastery ★
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This chapter has no Short on the channel yet, so ten empty cards are not shown. The notes, diagrams and checks are complete.
📄 PDF download — notes + answer key
Data and Activity 1
आँकड़े और क्रियाकलाप 1 · Textbook 14.1–14.2 · Exercise 14.1
Two meanings, then collectionNotes
Statistics is sometimes the plural of data and sometimes the subject that teaches collection, presentation, analysis and conclusions. Facts or numbers gathered for a purpose are data.
Gather them yourself and they are primary. Take them from a register or a news report and they are secondary. Range = largest − smallest. A count with no purpose does not become data.
Activity 1 and Exercise 14.1Activity
Divide the class into four groups. One group gathers the heights of 20 students, the second the absences of a month, the third the number of family members, the fourth the heights of 15 plants. Exercise 14.1 says: write five everyday data sets and call each primary or secondary.
Worked exampleExample
Question: The heights are 140, 152, 148 and 161 cm. Find the range.
Formula: range = largest value − smallest value.
Substitution: 161 − 140 = 21.
Unit: centimetre.
10-second revision
- Data are gathered for a purpose
- Gathered by you means primary
- Range = largest − smallest
Board tip · BSEBBoard tip
A copy from a register is secondary, even if you made the table.
Board tip · CBSEBoard tip
Write the unit with the range. Only 21 is incomplete if the data are in centimetres.
Check your understandingall correct = mastery ★
2
Data taken from a newspaper table are secondary.
Explanation:
True.
3
The range of the values 140 and 161 cm is ______ cm.
💡 Hint:
161−140.
Explanation:
21 cm.
4
The first job of Activity 1 is —
💡 Hint:
The first of the four groups.
Explanation:
Heights of 20 students.
5
Write one primary and one secondary example. Also give the range formula.
Model answer (board format)
Measuring the class heights yourself is primary. A price from a newspaper is secondary. Range = largest − smallest.
Check your answer:
A frequency table
बारंबारता सारणी · Textbook 14.3 · Activity 2 · Exercise 14.2
How often, that is the frequencyNotes
An ungrouped table writes the count beside each value. If the values are many, make classes. Keep a convenient class size and take the first interval as the book says. In 0–5, the 5 is often not included, when the book says so.
Tally marks keep the count honest. The greatest frequency is the common class. The least is the rare one. The total must equal the number of observations.
Activity 2 and Exercise 14.2Activity
The same four groups now turn their tables into frequencies. Choose the class size by looking at the range. Exercise 14.2 asks for tables such as blood groups, engineers’ distances (class size 5, first interval 0–5), humidity and heights. The 5 is not included if the book says so.
Worked exampleExample
Question: The values are 2, 3, 2, 5, 3, 2. Write the frequency of 2 and the total.
Formula: frequency = the count of that value. Total = the sum of all frequencies.
Substitution: 2 appears three times. The total of observations is 6.
Unit: a count, no other unit.
10-second revision
- Frequency is a count
- In 0–5, 5 is often outside
- The sum equals the total
Board tip · BSEBBoard tip
In the classes 0–5 and 5–10, put 5 in the second class when the book says 5 is not included.
Board tip · CBSEBoard tip
After the tally, write the number. Marks alone are not taken as the answer.
Check your understandingall correct = mastery ★
1
Frequency is —
💡 Hint:
How often.
Explanation:
The count.
2
The sum of the frequencies in a table must equal the number of observations.
Explanation:
True.
3
In 2, 3, 2, 5, 3, 2 the frequency of 2 is ______.
💡 Hint:
Three times.
Explanation:
3.
4
In the classes 0–5 (5 not included) and 5–10, which class gets the number 5? Give the reason in one line.
Model answer (board format)
5 goes in the second class 5–10, because the first interval does not include 5.
Check your answer:
Bar graphs and Activity 3
दंड आलेख और क्रियाकलाप 3 · Textbook 14.4 · Activity 3
Gaps stay between the barsNotes
A bar graph is good for separate names or classes. The length of a bar is proportional to the value. A gap is kept between the bars. Show every width the same, but the width is not used in the calculation.
Write the scale on the axis. Starting at zero keeps the picture honest. For two tables, keep one scale.
Activity 3Activity
The same four groups draw a suitable bar graph of their data. Do not push the height group and the family group into one picture if the units differ. The bar questions of Exercise 14.3 use this idea, but they come after the next lesson.
Worked exampleExample
Question: One bar stands for 12 students and the scale is 1 cm = 4 students. Find the length of the bar.
Formula: length = number ÷ one part of the scale.
Substitution: 12 ÷ 4 = 3.
Unit: centimetre.
10-second revision
- Length is proportional to the value
- A gap between the bars
- Write the scale on the axis
Board tip · BSEBBoard tip
Starting the axis away from zero makes a small gap look large. Start at zero.
Board tip · CBSEBoard tip
Do not change the value by changing the width. In a bar graph the width carries no meaning.
Check your understandingall correct = mastery ★
1
In a bar graph, between the bars there is —
💡 Hint:
Touching rectangles belong to a histogram.
Explanation:
A gap.
2
The length of a bar is proportional to the value.
Explanation:
True.
3
If 1 cm = 4 students, the bar for 12 students is ______ cm.
💡 Hint:
12÷4.
Explanation:
3 cm.
4
Activity 3 draws —
💡 Hint:
The third activity.
Explanation:
A bar graph.
5
The scale is 1 cm = 5 marks and the value is 20. Write the length of the bar.
Model answer (board format)
Length = 20 ÷ 5 = 4 cm.
Check your answer:
6
Changing the width in a bar graph changes the value.
Explanation:
False — the length shows the value. The width is kept the same.
Histogram and unequal widths
आयतचित्र और असमान चौड़ाई · Textbook 14.4 · continuous classes
Area is proportional to frequencyNotes
A histogram is the graph of a table of continuous classes. The rectangles touch. There is no gap. If the widths are equal, the length may be proportional to the frequency.
If the width changes, look at the area. Choose the smallest width. Rectangle length = (frequency ÷ class width) × minimum width. Drawing the raw frequency alone gives a wrong picture.
Worked exampleExample
Question: The minimum width is 10. One class has width 20 and frequency 8. Find the rectangle length.
Formula: length = (frequency ÷ width) × minimum width.
Substitution: (8 ÷ 20) × 10 = 4.
Unit: the length unit of the graph.
10-second revision
- The rectangles touch
- Area ∝ frequency
- Unequal width needs an adjusted length
Board tip · BSEBBoard tip
Do not turn frequency 8 of width 20 into height 8. Show (8/20)×10 = 4.
Board tip · CBSEBoard tip
Do not mix a bar graph and a histogram in one sentence. A gap means bars. Touching means a histogram.
Check your understandingall correct = mastery ★
1
In a histogram of continuous classes the rectangles —
💡 Hint:
No gap.
Explanation:
They touch.
2
The area of a rectangle is proportional to the frequency.
Explanation:
True.
3
If the width is 20, the frequency is 8 and the minimum width is 10, the length is ______.
💡 Hint:
(8/20)×10.
Explanation:
4.
4
If the widths are equal, the length may be kept —
💡 Hint:
The area stays right on its own.
Explanation:
Proportional to the frequency.
5
Width 30, frequency 9, minimum width 10. Write the length with the formula.
Model answer (board format)
Length = (9/30)×10 = 3.
Check your answer:
Frequency polygon and Exercise 14.3
बारंबारता बहुभुज और अभ्यास 14.3 · Class mark · Exercise 14.3
Join the midpointsNotes
The midpoints of the tops of the rectangles are the class marks. Class mark = (lower limit + upper limit) / 2. Join them. Assume one imaginary class of frequency zero on each side, and the polygon closes.
A polygon can also be drawn without a histogram. For comparing two sections, two polygons on one axis work well. Exercise 14.3 asks for bars, histograms and polygons.
Exercise 14.3Activity
The order starts with the bar questions, then histograms and polygons. Compare two groups with two polygons. Find the class marks and plot the points. Put an imaginary zero class at both ends.
Worked exampleExample
Question: Find the class mark of the class 10–20.
Formula: class mark = (lower limit + upper limit) / 2.
Substitution: (10 + 20) / 2 = 15.
Unit: the unit of the data.
10-second revision
- Class mark is the average of the two limits
- The polygon closes on zero classes
- The mark of 10–20 is 15
Board tip · BSEBBoard tip
The mark of 20–30 is 25, not 20 or 30. Show the average.
Board tip · CBSEBoard tip
The imaginary class has frequency 0. Do not count it as real data.
Check your understandingall correct = mastery ★
1
The mark of the class 20–30 is —
💡 Hint:
(20+30)/2.
Explanation:
25.
2
A frequency polygon joins the class marks.
Explanation:
True.
3
The mark of the class 10–20 is ______.
💡 Hint:
The average.
Explanation:
15.
4
How will you close the polygon down to the axis? One sentence.
Model answer (board format)
Join the marks of imaginary classes of frequency 0 on both sides.
Check your answer:
The mean
माध्य · Textbook 14.5 · ungrouped and frequency
Divide the sum by the countNotes
The ungrouped mean is x̄ = (sum of all values) / n. In a frequency table, x̄ = Σ(f x) / Σf. x is the value or the class mark, and f is its frequency.
One very large salary pulls the mean up. Then the mean is not a good representative of the group. The salary table of Exercise 14.4 points to this. The unit is the unit of the data.
Worked exampleExample
Question: The values are 4, 6, 6, 7 and 17. Find the mean.
Formula: x̄ = (Σx) / n.
Substitution: sum = 40, n = 5, x̄ = 40 / 5 = 8.
Unit: the unit of the values.
10-second revision
- x̄ = sum / n
- In a table, Σfx / Σf
- The mean of 4, 6, 6, 7, 17 is 8
Board tip · BSEBBoard tip
Writing only the sum and forgetting to divide by n is half an answer.
Board tip · CBSEBoard tip
In a frequency mean, multiply each value by f. Adding only the x values is wrong.
Check your understandingall correct = mastery ★
1
The ungrouped mean is —
💡 Hint:
The average.
Explanation:
Sum / n.
2
The mean of a frequency table is Σ(fx) / Σf.
Explanation:
True.
3
The mean of 4, 6, 6, 7, 17 is ______.
💡 Hint:
40/5.
Explanation:
8.
4
One very large value pulls the mean —
💡 Hint:
The salary example.
Explanation:
Upwards.
5
Values 2, 3, 7. Write the mean with the formula.
Model answer (board format)
x̄ = (2+3+7)/3 = 12/3 = 4.
Check your answer:
6
When finding the mean we do not divide by n.
Explanation:
False — the division is what makes the mean.
Median, mode, and Exercise 14.4
माध्यिका, बहुलक और अभ्यास 14.4 · Textbook 14.5 · Exercise 14.4
Order first, then the middleNotes
For the median, put the values in increasing order. If n is odd, the median is the value at place (n+1)/2. If n is even, average the (n/2)th and the next. The mode is the value that appears most often. There can be two modes.
Exercise 14.4 asks for goals, marks, an ordered list with x, the mode of one list, the mean of a salary frequency table, and when the mean is right and when the median is better.
Exercise 14.4 in orderActivity
1) Goals of ten matches: mean, median, mode. 2) All three for fifteen marks. 3) If the median of an increasing list is 63, find x. 4) The mode of the given list. 5) The mean of the salary table of 60 workers, by Σfx / Σf. 6) One situation where the mean is right and one where the median is better.
Worked exampleExample
Question: Find the median and the mode of 4, 6, 6, 7, 17.
Formula: n = 5 is odd, so the place is (5+1)/2 = 3. The mode is the most frequent.
Substitution: The list is already increasing. The third value is 6. 6 appears twice, so the mode is 6.
Unit: the unit of the values.
10-second revision
- For odd n, the ((n+1)/2)th
- For even n, the average of two middles
- Mode is the most frequent
Board tip · BSEBBoard tip
Write the order before the median. Without the order the middle place catches the wrong value.
Board tip · CBSEBoard tip
Mean 8 and median 6 belong to the same list. The large 17 pulls the mean. Write both.
Check your understandingall correct = mastery ★
1
The median of five increasing values is —
💡 Hint:
(5+1)/2 = 3.
Explanation:
The third.
2
The mode is the value that appears most often.
Explanation:
True.
3
The median of 4, 6, 6, 7, 17 is ______.
💡 Hint:
The third place.
Explanation:
6.
4
If n = 10 is even, the median is —
💡 Hint:
Two middles.
Explanation:
The average of the 5th and the 6th.
5
Write the mean, median and mode of 4, 6, 6, 7, 17. Which one does the large value pull?
Model answer (board format)
Mean = 40/5 = 8. Median = 6. Mode = 6. 17 pulls the mean upwards.
Check your answer:
❓ Full question bank — with answers and explanations — 66 questions
Pick a type. The 35 lesson checks are separate — each lesson has as many as its topic needs. All correct earns mastery ★.
BSEB modelpractice · not annual60 tried · 0 correctMultiple choiceMCQ130 tried · 0 correctTrue / falseTrue / false80 tried · 0 correctFill in the blanksFill80 tried · 0 correctMatchMatch20 tried · 0 correctAssertion–reasonAssertion–reason50 tried · 0 correctBalancingBalancing40 tried · 0 correctIdentifyIdentify20 tried · 0 correctShort and longVSA, SA, LA120 tried · 0 correctCBSE-stylenot a PYQ60 tried · 0 correct
No question is marked as a verified past paper. The BSEB set is a model for practice. CBSE items are CBSE-style, not a copy of any year’s paper.
Multiple choice
0/13Pick one option. A wrong try brings a hint.
1
Data you gather yourself are —
💡 Hint:
Your own purpose.
Explanation:
Primary.
2
The range is —
💡 Hint:
The difference.
Explanation:
Largest − smallest.
3
If 0–5 does not include 5, then 5 goes —
💡 Hint:
The limit rule.
Explanation:
Into 5–10.
4
A bar graph has —
💡 Hint:
A histogram touches.
Explanation:
Gaps.
5
In a histogram the rectangles —
💡 Hint:
Continuous classes.
Explanation:
They touch.
6
For width 20, f = 8 and minimum 10, the length is —
💡 Hint:
(8/20)×10.
Explanation:
4.
7
The mark of class 10–20 is —
💡 Hint:
The average.
Explanation:
15.
8
The ungrouped mean is —
💡 Hint:
Divide the sum.
Explanation:
Σx / n.
9
The frequency mean is —
💡 Hint:
Each value × its count.
Explanation:
Σ(fx) / Σf.
10
For n = 5 the median place is —
💡 Hint:
(5+1)/2.
Explanation:
The third.
11
The mode is —
💡 Hint:
The greatest count.
Explanation:
The most frequent value.
12
The mean of 4, 6, 6, 7, 17 is —
💡 Hint:
40/5.
Explanation:
8.
13
The median for even n = 10 is —
💡 Hint:
Two middles.
Explanation:
The average of the 5th and the 6th.
True or false
0/81
Secondary data are measured by the investigator.
Explanation:
False — measuring yourself is primary.
2
The sum of frequencies must equal the number of observations.
Explanation:
True.
3
A bar graph and a histogram are the same picture.
Explanation:
False — one has gaps, the other has touching rectangles.
4
For unequal widths the raw frequency is the height.
Explanation:
False — the length is (f / width) × minimum width.
5
The class mark is the average of the two limits.
Explanation:
True.
6
One very large value pulls the mean up.
Explanation:
True.
7
Order is not needed before the median.
Explanation:
False — increasing order comes first.
8
There can be more than one mode.
Explanation:
True — two values can appear most often, equally.
Fill in the blanks
0/81
161 − 140 = ______ cm.
💡 Hint:
The range.
Explanation:
21.
2
In 2, 3, 2, 5, 3, 2 the frequency of 2 is ______.
💡 Hint:
The count.
Explanation:
3.
3
For 12 students and 1 cm = 4, the bar is ______ cm.
💡 Hint:
12/4.
Explanation:
3.
4
(8/20)×10 = ______.
💡 Hint:
Unequal width.
Explanation:
4.
5
(10+20)/2 = ______.
💡 Hint:
Class mark.
Explanation:
15.
6
40/5 = ______.
💡 Hint:
The mean.
Explanation:
8.
7
For n = 5 the median place is ______.
💡 Hint:
(5+1)/2.
Explanation:
3.
8
The mode of 4, 6, 6, 7, 17 is ______.
💡 Hint:
Twice.
Explanation:
6.
Match
0/21
Match the measure with its meaning.
Column B: A. Largest − smallest · B. Sum / n · C. The middle value · D. Most frequent
1. Mean
2. Median
3. Mode
4. Range
Explanation:
Mean is the average, median the middle, mode the most frequent, range the difference.
2
Match the activity with its job.
Column B: A. Mean, median, mode · B. Gathering four kinds of data · C. A frequency table · D. A bar graph
1. Activity 1
2. Activity 2
3. Activity 3
4. Exercise 14.4
Explanation:
1 is collection, 2 is the table, 3 is the bar graph, and 14.4 is the three measures.
Assertion–reason
0/5Check both statements, then see whether the reason explains the assertion.
1
Assertion (A): The rectangles of a histogram touch.
Reason (R): It is the graph of continuous classes and the area is proportional to the frequency.
Explanation:
Both are true and R is the reason.
2
Assertion (A): Mean = sum / n.
Reason (R): The mode is the most frequent value.
Explanation:
Both are true, but R does not explain the mean.
3
Assertion (A): For unequal widths the length is adjusted.
Reason (R): The raw frequency is always the height.
Explanation:
A is true. R is false.
4
Assertion (A): Primary data are copied from a newspaper.
Reason (R): Secondary data come from another source.
Explanation:
A is false. R is true.
5
Assertion (A): The median of 4, 6, 6, 7, 17 is 6 and the mean is 8.
Reason (R): 17 pulls the mean up, not the middle place.
Explanation:
Both are true and R is the reason.
Coefficient practice
0/4These are not results of this maths chapter. They are only coefficient practice for H2 + O2 → H2O.
1
This is coefficient practice, not a result of this maths chapter. Fill coefficients for H2 + O2 making H2O (blank = 1). This is not a statistics result.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O
2
This is coefficient practice, not a result of this maths chapter. Fill coefficients for H2 + O2 making H2O (blank = 1). Match the hydrogen count.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O
3
This is coefficient practice, not a result of this maths chapter. Fill coefficients for H2 + O2 making H2O (blank = 1). Match the oxygen count.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O
4
This is coefficient practice, not a result of this maths chapter. Fill coefficients for H2 + O2 making H2O (blank = 1). A blank coefficient is 1.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O
Classify
0/21
Place each picture in its type.
Gaps between bars
Touching rectangles
Width carries no meaning
Area proportional to frequency
Explanation:
Gaps mean a bar graph. Touching rectangles and area mean a histogram.
2
Place each measure on its name.
Sum / n
The middle place
Most frequent
Σfx / Σf
Explanation:
The sum and Σfx are the mean. The middle is the median. The most frequent is the mode.
Very short answer
0/51
Define primary data in one line.
Model answer (board format)
Data the investigator gathers for a purpose of their own are primary.
Check your answer:
2
Write the range formula.
Model answer (board format)
Range = largest value − smallest value.
Check your answer:
3
Write the class-mark formula.
Model answer (board format)
(lower limit + upper limit) / 2.
Check your answer:
4
Write the ungrouped mean formula.
Model answer (board format)
x̄ = (Σx) / n.
Check your answer:
5
Write the median place for odd n.
Model answer (board format)
The ((n+1)/2)th place.
Check your answer:
Short answer
0/41
Find the mean, median and mode of 4, 6, 6, 7, 17.
Model answer (board format)
Mean 8, median 6, mode 6.
Check your answer:
2
Width 20, frequency 8, minimum width 10. Write the rectangle length.
Model answer (board format)
(8/20)×10 = 4.
Check your answer:
3
Write the mark of class 30–40 and the bar length for value 20 when 1 cm = 5 marks.
Model answer (board format)
The mark = 35. Length = 20/5 = 4 cm.
Check your answer:
4
Write the mean and median of 10, 10, 40. Which is the better representative?
Model answer (board format)
Mean = 60/3 = 20. Median = 10. 40 pulls the mean, so the median is the better representative.
Check your answer:
Long answer
0/31
Write the difference between primary and secondary data, and between a bar graph and a histogram. Also find the range of 161 and 140.
Model answer (board format)
Gathering yourself is primary. Taking from a source is secondary. A bar graph has gaps. A histogram touches. Range = 21 cm.
Check your answer:
2
Write the definitions of mean, median and mode. Give all three for 4, 6, 6, 7, 17.
Model answer (board format)
Mean is sum/n, median is the middle, mode is the most frequent. The values are 8, 6 and 6.
Check your answer:
3
Write Activity 1, 2, 3 and Exercises 14.1 to 14.4 in order, one line each.
Model answer (board format)
1 collection. 14.1 primary or secondary. 2 frequency table. 14.2 tables. 3 bar graph. 14.3 graphs. 14.4 mean, median, mode.
Check your answer:
BSEB model paper · practice
0/6This model set is for practice. It is not a question from any year’s annual examination. Annual questions will be added only when a source page is available.
1
The mark of class 40–50 is —
💡 Hint:
The average.
Explanation:
45.
2
On unequal widths the histogram height depends on —
💡 Hint:
The area.
Explanation:
Frequency and width.
3
The mean of 2, 3, 7 is ______.
💡 Hint:
12/3.
Explanation:
4.
4
Activity 3 is a bar graph.
Explanation:
True.
5
Write the median and the mean of 10, 10, 40. Which one is pulled?
Model answer (board format)
Median 10. Mean 20. 40 pulls the mean.
Check your answer:
6
This is coefficient practice, not a result of statistics. Balance H2 + O2 making H2O by filling coefficients (blank = 1).
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O
CBSE-style questions
0/6These are competency-based practice questions. They are not copies of a CBSE paper.
1
A student who graphs a newspaper table should call the data —
💡 Hint:
The source is someone else.
Explanation:
Secondary.
2
In a clinic one bill is very large. For a typical expense the better measure is —
💡 Hint:
The mean gets pulled.
Explanation:
The median.
3
Assertion (A): A histogram has no gap between rectangles.
Reason (R): So the width never matters.
Explanation:
A is true. R is false — for unequal widths the length changes.
4
Hiding the scale and making a bar look twice as long is a fair comparison.
Explanation:
False — write the scale on the axis and start at zero.
5
A shop’s sales are 8, 8, 9, 10 and 40 thousand rupees. Find the mean and the median. Which will you tell the manager?
Model answer (board format)
Sum 75, mean 15. Median 9. One large day pulled the mean, so the median tells the fairer story. The unit is thousand rupees.
Check your answer:
6
How is measuring the class height yourself different from copying a register? Which group of Activity 1 is the first kind?
Model answer (board format)
Measuring yourself is primary. A register is secondary. The height group is a primary collection.
Check your answer:
🏛️ Board exam corner — Bihar Board (BSEB)— CBSE
Switch board with BSEB | CBSE above. The lessons follow the same NCERT chapter.
BSEB model · practiceBoard tip
This page has no verified annual-exam question, because no source page has been added. The model set below is practice in the board pattern.
🏛️ Model questions on one page →
The verified label will be used only when a source page for the question is available.
CBSE-style · competency-based
These are case and assertion-reason practice items. Do not treat them as past CBSE questions.
🔁 Spaced review — today’s questions
Wrong questions return soon; correct ones return after a few days.
🧠 What you learned + equation sheet
What you learned
- Data are facts or numbers collected for a purpose.
- Primary data are gathered by you. Secondary data come from a source.
- A bar graph has gaps. The rectangles of a histogram touch.
- For unequal widths the rectangle length depends on both frequency and width.
- Class mark = (lower + upper) / 2. The polygon joins these marks.
- Mean is sum ÷ count, median is the middle value, mode is the most frequent value.
| What | Keep this |
|---|---|
| Mean | Σx / n |
| Median | middle value |
| Mode | most frequent |
| Class mark | (lower+upper)/2 |
| Histogram | areas ∝ frequency |
| Unequal width | (f / width) × min width |
The notes are original writing. The textbook was used only for activity order and numbers. “Verified” will be used only on a question that has a source page.