Best Guess · Puzzle #1 · Wednesday, September 30
Best Guess: the answers
Four questions, each with one true number. Here they are with their answers, how to reason each one out, and where the number comes from. Play today's Best Guess.
1. How many species of plants, animals, fungi and other complex (eukaryotic) life are estimated to exist on Earth?
The answer: about 8.7 million. By this estimate, about 86% of species on land and 91% in the ocean have not yet been described.
Napkin math: Scientists have described a bit over a million species, and most of the planet's insects and fungi are still undiscovered.
Source: PLOS Biology (via Europe PMC), How many species are there on Earth and in the ocean?
2. How many Dollar General stores were operating as of late February 2026?
The answer: 20,959. All but 17 of them are in the US, spread across 48 states.
Napkin math: If most of about 20,000 small towns and neighborhoods in the US have one, that's in the tens of thousands.
3. How far from Earth does the James Webb Space Telescope orbit, in miles?
The answer: about 1 million miles. Hubble, by contrast, orbits just 560 kilometers above Earth; Webb instead orbits the Sun at the second Lagrange point, L2.
Napkin math: It sits well beyond the Moon (about 239,000 miles away) at a gravitational balance point, roughly four Moon-distances out.
4. How many monthly active users did Spotify have in mid-2026?
The answer: 777 million. 300 million of them pay for Premium, a milestone Spotify says no audio streaming service had reached before.
Napkin math - 8Bpeople on Earth
- ÷10people for each monthly Spotify user
≈800Musers
Source: Spotify, Spotify Reports Second Quarter 2026 Earnings