Hinglish

Data Detective

Class 7 Maths · Chapter 13: Connecting the Dots… · NCERT Ganita Prakash section P2 5.4

Learn

Well-organised data tells stories and raises mysteries. Dot plots of heights in two schools show Classes 6 to 8 in one school are much taller on average. Why? Where are the schools? Data from two schools is not enough to say anything about all children.

A survey table of average heights in India, 1989 to 2019, lets us check claims. Justified: "13-year-old boys' average height rose from 144 to 148 cm." Not justified: "all 13-year-old girls are taller than all 11-year-olds": averages describe groups, not every person.

Look for trends: girls' average heights grew fastest around ages 10–12, boys' around 12–14. A zoomed axis (starting at 145 cm instead of 0) shows small differences clearly, but read the scale carefully so you do not exaggerate them.

A mean decision? Making a door to fit the average height of a family would leave the tallest bumping their heads! Choosing the right summary (mean, median, maximum) depends on the question you are answering.

Explore: justified or not?

  1. Sort the claims about the height survey.

Remember

  • Use data to justify claims; averages describe groups, not every individual.
  • Choose the summary that fits the question: mean, median, or an extreme value.

Quick check

Door height for a family: which summary should decide it?

  1. the tallest person's height (plus a margin)
  2. the mean height
  3. the median height
  4. the shortest height
Answer

the tallest person's height (plus a margin). Everyone must fit, so the maximum matters here, not the centre.

Think about it

17 students' heights are given. How can the teacher split them into two equal groups of shorter and taller students?

One answer

Sort the heights and find the median (the 9th value). The 8 below it form one group and the 8 above it the other; the median student can join either (or 16 students split 8–8).

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.