Collection of logic puzzles

These are puzzles in which only logic is required. You might need to count, compare small numbers, or other such things, but you'll never need a special skill, such as long division, or theorem, such as the Pythagorean theorem.


Three Spinners by NRICH

Here's the solution: Start by writing down the numbers for each spinner. We know 7 of the red numbers, 8 of the blue, and 8 of the yellow. Look at the first set of unknown numbers. 4 of them: 3, 5, 7, 9, are not red numbers. But we know 7 of the red numbers. Thus, the first set of unknown numbers can't be red. Again looking at the first set of unknown numbers, 3 of them: 5, 7, 9, are not yellow numbers. But we know 8 of the yellow numbers. Thus, the first set of unknown numbers can't be yellow either. Looking at the first set of unknown numbers again, 2 of them: 1 and 13, are not blue numbers. We know 8 of the blue numbers, so the two missing blue numbers must have been 1 and 13. The solution continues in this way.