Mr. Math is between 50 and 80 years old. If you divide his age by 9, the remainder is 1. If you divide his age by 4, the remainder is 1. How old is Mr. Math?

Work with the larger number (9) first. What numbers, when divided by 9, leave a remainder of 1? Then take those answers, and see of any of them, when divided by 4, give a remainder of 1. (Yes, there is one.)