CBSE Class 8 Maths — Data Handling

Chapter Overview & Weightage

Data Handling is a scoring chapter in CBSE Class 8 Maths. It introduces students to organising, representing, and interpreting data — skills that appear across subjects and in real life.

Topics covered:

• Frequency distribution tables (grouped and ungrouped data)
• Bar graphs, double bar graphs
• Pie charts (circle graphs) and their construction
• Histograms and frequency polygons
• Introduction to probability

Key Concepts You Must Know

1. Frequency Distribution Raw data organised into classes (intervals) with their frequencies. A class width should be uniform throughout the table. The class mark (midpoint) = (lower limit + upper limit) / 2.

2. Bar Graphs and Double Bar Graphs Bar graphs represent discrete data with uniform-width bars and gaps between them. Double bar graphs compare two data sets side by side.

3. Pie Charts Each sector angle = $\frac{\text{frequency}}{\text{total frequency}} \times 360°$

4. Histograms Like bar graphs, but for continuous grouped data. No gaps between bars. The width of each bar represents the class interval.

5. Frequency Polygons Formed by joining the midpoints of the top of each histogram bar with straight lines. Useful for comparing two distributions on the same graph.

6. Probability

Probability always lies between 0 and 1. $P(\text{impossible event}) = 0$, $P(\text{certain event}) = 1$.

Important Formulas

Solved Previous Year Questions

PYQ 1 — Pie Chart Construction (CBSE 2023 Style)

The favourite sports of 36 students: Cricket 15, Football 10, Hockey 7, Badminton 4. Draw a pie chart.

Solution:

Draw a circle, mark the centre, and construct each sector with the calculated angle using a protractor.

PYQ 2 — Probability

A bag contains 5 red, 3 blue, and 2 green balls. If one ball is drawn at random, find: (a) P(red ball) (b) P(blue ball) (c) P(not green ball)

Solution: Total balls = 5 + 3 + 2 = 10

(a) $P(\text{red}) = 5/10 = 1/2$

(b) $P(\text{blue}) = 3/10$

(c) P(not green) = P(red or blue) = $8/10 = 4/5$

Or use: P(not green) = 1 − P(green) = 1 − 2/10 = 8/10 = 4/5

PYQ 3 — Histogram Reading

A histogram shows the marks of 40 students in groups 20–30, 30–40, 40–50, 50–60, 60–70 with frequencies 5, 8, 12, 10, 5. Find: (a) modal class (b) number of students scoring at least 50.

Solution: (a) Modal class = 40–50 (highest frequency = 12) (b) Students scoring ≥ 50: frequency of 50–60 + 60–70 = 10 + 5 = 15 students

Difficulty Distribution

About 70% of marks in this chapter come from Easy or Medium questions — this is truly a scoring chapter if you practice construction regularly.

Expert Strategy

For pie charts: Always make a table first with the angle calculation column. If your angles don’t add to 360°, you’ve made an arithmetic error — find it before drawing. Use a sharp pencil and protractor for the diagram.

For histograms: Remember there are NO gaps between bars (unlike bar graphs). The x-axis must show the class limits, not labels. Draw bars from the exact lower limit to the upper limit.

For probability: List all possible outcomes first (the sample space). Don’t assume — count. In a die, outcomes are 1, 2, 3, 4, 5, 6 — there are exactly 6, not more.

Common Traps