2QUESTION 2 OF 3
Answer & explanation
The official answer, with Fermi’s reasoning step by step.
Answer & explanation
Official answer
180,000,000
people
How to estimate it
Fermi’s official “Napkin math”
Start with the world population today, about 8.2 billion. Life expectancy in a lot of the world barely reaches 80, so guess only a small slice make it that far, maybe 1 in 45 people.
- World population, 2026 (known)
- 8,200,000,000
- Guessed share aged 80 or older
- ≈ 1 in 45
- ≈ result
- ≈ 182,000,000
Rounded assumptions may give a slightly different estimate. The official answer above is the game’s reference value.
Source calculation & reference
- Global population aged 80+, 2021 (UN World Population Prospects, 2024 revision)
- 152,900,000
- Growth in that cohort (UN projects about 426 million by 2050)
- ≈ 3.5% a year
- 152.9 million compounded forward 5 years
- ≈ 180,000,000
Reference cited by Fermi: UN World Population Prospects, 2024 revision
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.