3QUESTION 3 OF 3
Answer & explanation
The official answer, with Fermi’s reasoning step by step.
Answer & explanation
Official answer
1,500,000,000
children
How to estimate it
Fermi’s official “Napkin math”
The easiest place to start is the world population, about 8 billion. How much of that is kids? Maybe a quarter of everyone is under 15, and most of those are 10 or younger, so call it three quarters of that slice.
- World population, roughly
- 8,000,000,000
- Share under 15
- × 1/4
- Share of that group aged 10 or younger
- × 3/4
- ≈ result
- 1,500,000,000
Rounded assumptions may give a slightly different estimate. The official answer above is the game’s reference value.
Source calculation & reference
- World population, 2024 (UN estimate)
- 8,200,000,000
- Share aged 0-14 (UN World Population Prospects 2024)
- ~25%
- Share of that band aged 0-10 (11 of 15 single-year cohorts)
- ~73%
- ≈ result
- 1,500,000,000
Reference cited by Fermi: United Nations World Population Prospects 2024 age-structure data, cross-checked against UNICEF under-5 population estimates
How close was your guess?
Your comparison will appear here.
Compare by ratio: divide the larger number by the smaller one. The closer to 1×, the better.