+1839 We call a number cozy if every digit in the number is either even or next to an even digit. For example, a number is cozy if every digit in the number is either a 2 or next to a 2. For example, the number 222, 72, 45, and 810 and are all cozy. Also, the numbers 202 and 2772 are cozy.
How many 2-digit numbers are cozy?
+34 Any two-digit number with a 2 is cozy (and all cozy numbers have at least one 2) There are nine two-digit numbers with ones digit 2 and there are nine additional two-digit numbers with tens digit 2 (excluding 22 which we've already counted, since its ones digits is 2) Therefore, there are 9 + 9 = 18 cozy two-digit numbers.
