Solution to: Notable Number
The number we are looking for is divisible by both 9 and 11. Since 11 is a prime number, the number we are looking for has to be a multiple of 9 × 11 = 99. There are only nine possibilities, because 2 × 99 = 198 is the smallest number with three digits that is divisible by 99, and 10 × 99 = 990 is the largest number with three digits that is divisible by 99. The solution is 891, because 198 = 2/9 × 891.
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