Try this little math puzzle.

Suppose you have a four digit number. The first digit is 1/5 of the last digit and the second and third digit together is 3 times the last digit. What is the number? (hint, the sum of the digits is 12)

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The answer it 1155.  The last digit must be a multiple of 5 since the first digit is 1/5. So the last digit must be 5 and the first digit must be 1.  The tricky part at first reading this is that the second and third digit being 3 times the last, you might think the second digit is 15 and the third is also 15, but that makes no sense, because a digit is a single number. the 2nd and third TOGETHER is 15, so 1 in the second digit and 5 in the third. So the answer is 1155.