How scoring works
Points for being right and sure.
Every question asks for a range. The score rewards ranges that catch the answer, and rewards narrow ones more.
The rule
- Inside your range: up to 10 points. A range from 100 to 1,000 is one "power of ten" wide and scores 6.7; from 100 to 10,000 scores 3.3; exact (low = high) scores 10; a range 1,000 times wide or more scores 0.
- Outside your range: 0 points, however close.
- Eight questions a day, so a perfect day is 80.
Why 80%?
Most people's "pretty sure" is less sure than they think. In classic estimation studies (Alpert and Raiffa; Russo and Schoemaker, Decision Traps, 1989), ranges people called 90% or 98% sure caught the true answer far less often than 9 times in 10. Aiming for 80% and checking it with the Nitwit Meter is the quickest way to learn what your own "sure" is worth.
Where the answers come from
Every answer is calculated by the site from the numbers in the question: date arithmetic on the Gregorian calendar, powers of two, compound interest, exact probabilities, factorials and combinations. Nothing is looked up, so nothing is out of date. The working is shown under every result.
The ten families
- Calendar Days between two dates
- Clockwork Seconds, minutes and hours
- Doubling Things that double every day
- Interest Money left to grow
- Birthdays Shared-birthday odds
- Dice Chances with fair dice
- Head maths Big sums and products
- Folding Paper folded in half, again
- Orders Arrangements and choices
- Packing Cubes in a box
Typing numbers
Commas, a $ or a % are fine. 1.5k, 2 million, 3 billion, 4e12 and 4 x 10^12 all work. Ranges start above zero, and the biggest number accepted is 10^30. If you type the high end first, we swap them.