Collection of multiplication puzzles
Which number or numbers, from 0-100, are described by the clues below? Further, which clues, if any, are unnecessary?
- The number is greater than 9.
- The number is not a multiple of 10.
- The number is a multiple of 7.
- The number is odd.
- The number is not a multiple of 11.
- The number is less than 200.
- Its ones digit is larger than its ten digit.
- Its tens digit is odd.
With this puzzle, it's obvious the clues could be changed to yield more puzzles. The initial set of numbers could also be something different from 0-100. In fact, given the right clues, it needn't be finite either. For example, if the initial set is 0-infinity, and your clues are, the number is even and prime, then a unique number is described, namely, 2.
Source: What Do You Need? by NRICH
Lots more puzzles can be found here.