A teacher once told me that if you add any number’s digits and get a sum that is divisible by three, then that original number is divisible by three, too. Never again did I look at a number without running that equation in my head. The address 1535 Linscott became 1 + 5 + 3 + 5 = 14, which is not divisible by three, thus 1535 is not, either. License plate KLT 438 became 4 + 3 + 8 = 15, which is divisible by three, and thus so was 438.
