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NCERT Solutions for Class 7th Maths Chapter 5 Know Your Onions! — Math Talk

Book page 101 – 102 Updated on2026-09-19

Q1.
The table shows the monthly price of onions, in rupees per kilogram (kg), at two towns. Where are onions costlier, according to you?
MonthYahapurWahapur
Jan2519
Feb2417
Mar2623
Apr2830
May3038
Jun3535
Jul3942
Aug4339
Sep4953
Oct5660
Nov5952
Dec4442
Monthly price of onions, in rupees per kilogram, at the two towns — page 101.
Answer

Taken over the whole year, onions are slightly costlier in Yahapur — but the two towns are so close that the answer depends on which measure you use. That is the real point of the question.

MeasureYahapurWahapurCostlier
Total of the 12 prices₹458₹450Yahapur
Mean price458 ÷ 12 ≈ ₹38.17450 ÷ 12 = ₹37.50Yahapur
Median price(35 + 39) ÷ 2 = ₹37(38 + 39) ÷ 2 = ₹38.50Wahapur
Highest price₹59 (Nov)₹60 (Oct)Wahapur
Lowest price₹24 (Feb)₹17 (Feb)Yahapur (never as cheap)
Range (max − min)59 − 24 = ₹3560 − 17 = ₹43Wahapur swings more
Months with the higher price6 months5 monthsYahapur (1 month equal)
Why it happens: Yahapur wins on total, mean and number of dearer months; Wahapur wins on median and on the single highest price. Wahapur's prices are more spread out — very cheap in February (₹17), very dear in October (₹60) — so its low months pull its total down even though its peaks are higher.
Judging the children's claims: Khushboo ("Wahapur, it has the highest price ₹60") uses one month out of twelve. Vishal ("Wahapur has 3 numbers in the 50s") counts only part of the data. Jithin's remark about the range is not about costliness at all — it is about variability. Nafisa's totals and Sampat's month-by-month count are the two fairest comparisons, and both point mildly to Yahapur.
Q2.
Can you think of any other ways to compare the data?
Answer

Yes. Beyond the minimum, maximum, mean, total and range, here are ways a Grade 7 student can actually carry out.

  • Median — the middle price of each town: ₹37 for Yahapur, ₹38.50 for Wahapur.
  • Month-by-month differences — subtract the two prices each month and look at the pattern. In Jan–Mar Yahapur is dearer by ₹3–₹6; in Apr–Jul Wahapur is dearer.
  • Count how many months each town crossed ₹50: Yahapur 2 (Oct, Nov), Wahapur 3 (Sep, Oct, Nov).
  • Group the prices into bands — ₹11–20, ₹21–30, ₹31–40, ₹41–50, ₹51–60 — and count how many months fall into each band. This is what a dot plot shows at a glance.
  • Season by season — compare the mean of Jan–Jun with the mean of Jul–Dec for each town. Both towns are far dearer in the second half of the year.
  • Cost of a fixed purchase — if a family buys 2 kg every month, work out the year's onion bill: ₹916 in Yahapur, ₹900 in Wahapur.
Why it happens: a single number can only answer a single question. "Which town is dearer on the whole?" needs the mean or the total. "Which town is riskier for a shopkeeper?" needs the range. "When should we buy?" needs the month-by-month pattern.
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