3QUESTION 3 OF 3
Answer & explanation
The official answer, with Fermi’s reasoning step by step.
Answer & explanation
Official answer
60,000,000
people
How to estimate it
Fermi’s official “Napkin math”
Again, the best place to start is the world's population. How many humans are identical twins? It's rare, you might know one pair. Maybe 1 in 100 people.
- World population
- 8,000,000,000
- Identical twins
- ≈ 1 in 100
- 8B ÷ 100
- ≈ 80,000,000
Rounded assumptions may give a slightly different estimate. The official answer above is the game’s reference value.
Source calculation & reference
- Identical twin pairs per 1,000 deliveries, about the same everywhere (Monden, Pison and Smits, Human Reproduction 2021)
- ≈ 4
- Two babies per pair, so share of people born an identical twin
- ≈ 0.8%
- World population 8.2B × 0.8%
- ≈ 65,000,000
- Less twins' higher child mortality, rounded
- ≈ 60,000,000
Reference cited by Fermi: Monden, Pison and Smits, Human Reproduction (2021): about 4 identical pairs per 1,000 deliveries
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.