Several clues at once
Here's a puzzle: a two-digit number whose digits add to 12. The number is odd. Its tens digit is bigger than its ones digit. The tens digit is on the left. The ones digit is on the right.
- Digit sum 12: 39, 48, 57, 66, 75, 84, 93.
- Keep only the odd ones: 39, 57, 75, 93.
- Keep only tens bigger than ones: 75, 93.
- Two numbers survive. Both fit every clue.
Clues work in any order
Use the clues in any order. A clue removes the numbers that do not fit it. 75 and 93 are left each time.
The rule
Apply every clue. Keep only the numbers that pass all of them. Then count what survives. One left is the answer. Several left means the clues are not enough yet. None left means no number fits them all.
Some clues remove no number at all. "It is a multiple of 1" is true of every number. Add another clue: "a multiple of 5". Only 75 is left now.
Try the clue "the number is prime" instead. A prime has exactly two factors: 1 and itself. 75 = 3 × 25 and 93 = 3 × 31, so both fail. No number is left. That is a real answer too.
Tap clues on and off. Watch which ones remove a number.
Loading lab…