NCERT Solutions Ganita Prakash (Part 1) Chapter 1 –191.6 Did You Ever Wonder…? — In-text Questions

Book page 18 Updated on2026-09-05

Q1.

“Could the entire population of Mumbai fit into 1 lakh buses?” What do you think? How can we find out?

Answer

No, it could not. One lakh buses hold about 50 lakh people, but Mumbai has more than 1 crore 24 lakh.

Assume 1 bus holds 50 people.
1 lakh buses hold = 1,00,000 × 50
= 50,00,000 = 50 lakh people

Population of Mumbai (2011) = 1,24,42,373
1,24,42,373 > 50,00,000
Left standing = 1,24,42,373 − 50,00,000 = 74,42,373 people

Why it happens: The method is what matters — make a sensible assumption (50 seats per bus), multiply, then compare with the real figure. To fit all of Mumbai you would need 1,24,42,373 ÷ 50 ≈ 2,48,848 buses, nearly 2½ lakh.

Q2.

The RMS Titanic ship carried about 2500 passengers. Can the population of Mumbai fit into 5000 such ships?

Answer

Yes — just barely.

Capacity = 5000 × 2500
= 5 × 25 × 1000 × 100
= 125 × 1,00,000
= 1,25,00,000 people (1 crore 25 lakh)

Population of Mumbai = 1,24,42,373
1,24,42,373 < 1,25,00,000 ✓
Space to spare = 57,627 places

Why it happens: It is a very close call — the ships hold only about 58,000 more than Mumbai's population, less than half a percent extra. Had we used Mumbai's present-day population instead of the 2011 census figure, the answer might well flip to “no”.

Q3.

Roxie wondered, “If I could travel 100 kilometers every day, could I reach the Moon in 10 years?” (The distance between the Earth and the Moon is 3,84,400 km.) How far would she have travelled in a year? How far would she have travelled in 10 years?

Answer

No — after 10 years she would still be about 19,400 km short.

Distance in 1 year = 100 × 365
= 36,500 km

Distance in 10 years = 36,500 × 10
= 3,65,000 km

Distance to the Moon = 3,84,400 km
Short by = 3,84,400 − 3,65,000 = 19,400 km

Why it happens: Doing it in stages — first per year, then per 10 years — keeps the numbers small and manageable. You can use this staged method for any large calculation.

Check it yourself: How long would the whole trip take? 3,84,400 ÷ 36,500 ≈ 10.5 years — so a little over ten and a half years.

Q4.

Find out if you can reach the Sun in a lifetime, if you travel 1000 kilometers every day. (You had written down the distance between the Earth and the Sun in a previous exercise.)

Answer

No. The journey would take about 403 years — far more than a lifetime.

Distance to the Sun = 14,70,00,000 km (from page 16)
Distance in 1 year = 1000 × 365 = 3,65,000 km

Years needed = 14,70,00,000 ÷ 3,65,000
= 1,47,000 ÷ 365
≈ 402.7 years

Why it happens: A human lifetime is at most about 100 years, so you would cover only 100 × 3,65,000 = 3,65,00,000 km — roughly a quarter of the way. You would need four full lifetimes travelling 1000 km every single day.

Tip: Cancel the common zeroes before dividing: 14,70,00,000 ÷ 3,65,000 becomes 1,47,000 ÷ 365, which is much friendlier.

Q5.

Make necessary reasonable assumptions and answer the questions below: (a) If a single sheet of paper weighs 5 grams, could you lift one lakh sheets of paper together at the same time? (b) If 250 babies are born every minute across the world, will a million babies be born in a day? (c) Can you count 1 million coins in a day? Assume you can count 1 coin every second.

Answer

All three answers are no.

(a) Weight = 1,00,000 × 5 g
= 5,00,000 g = 500 kg
A person can lift perhaps 40–50 kg, so no — 500 kg is about the weight of 8 adults.

(b) Minutes in a day = 60 × 24 = 1,440
Babies in a day = 250 × 1,440 = 3,60,000
1 million = 10,00,000
3,60,000 < 10,00,000 → no, only about a third of a million.

(c) Seconds in a day = 60 × 60 × 24 = 86,400
So at most 86,400 coins a day.
86,400 < 10,00,000 → no, not even a tenth of a million.

Why it happens: Part (c) hides a very useful fact — a day is only 86,400 seconds. Counting a million things at one per second would take 10,00,000 ÷ 86,400 ≈ 11.6 days without a single break for sleep.

Try This: Make up your own questions in the same style. “Could all the students in your school stand shoulder to shoulder across a 1 km road?” “Would a lakh one-rupee coins fill your school bag?”

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