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NCERT Solutions Ganita Prakash (Part 1) Chapter 2 –382.5 Did You Ever Wonder? · Getting a Sense for Large Numbers — In-text Questions

Book page 37 Updated on2026-09-05

Q1.
The estimated global population of starlings is around 1.3 arab/1.3 billion (_________). [Fill in the blank in scientific notation.]
Answer

1.3 × 109

1 arab = 1,00,00,00,000 = 109
1 billion = 1,000,000,000 = 109
So 1.3 arab = 1.3 billion = 1.3 × 109 starlings

The row is headed 109, and the coefficient 1.3 lies between 1 and 10, so the entry is in proper standard form.

Why it happens: arab and billion are names for the same number, 109, reached by two different naming systems — the Indian one counting in hundreds (lakh, crore, arab) and the international one counting in thousands (thousand, million, billion). Powers of 10 let you write the quantity once and read it in either system.
Did you know? A starling murmuration is a mesmerising aerial display of thousands of starlings flying in synchronised, swirling patterns, often described as a "choreographed dance".
Q2.
With a global human population of about 8 × 10⁹ and about 4 × 10⁵ African elephants, can we say that there are nearly 20,000 people for every African elephant?
Answer

Yes.

People per elephant = (8 × 109) ÷ (4 × 105)
= (8 ÷ 4) × 109–5
= 2 × 104
= 20,000 people per elephant
Why it happens: dividing numbers in standard form splits into two easy halves — divide the coefficients (8 ÷ 4 = 2) and subtract the exponents (9 – 5 = 4). Neither half needs long division. Compare doing 8,00,00,00,000 ÷ 4,00,000 by hand, where the only real difficulty is keeping count of the zeros; the exponent does that counting for you.
Tip: when the coefficients divide awkwardly, round them. (8.2 × 109) ÷ (4.15 × 105) is still about 2 × 104 — the answer to the nearest power of 10 barely moves.
Q3.
The estimated mosquito population worldwide (2023) is 11 neel/110 trillion (________). [Fill in the blank in scientific notation.]
Answer

1.1 × 1014

1 neel = 1013, so 11 neel = 11 × 1013
1 trillion = 1012, so 110 trillion = 110 × 1012

11 × 1013 = 110 × 1012 = 1,10,00,00,00,00,00,000
In standard form = 1.1 × 1014

Compare with the Antarctic krill in the same row, 50 neel / 500 trillion = 5 × 1014 — nearly five times as many.

Why it happens: 11 × 1013 and 110 × 1012 are both correct values but neither is in standard form, because the coefficient must satisfy 1 ≤ x < 10. Shifting the decimal point one place left in 11 costs a factor of 10, which is paid back by raising the exponent from 13 to 14.
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