(this one is just for fun) a number is divisible by 3 if the sum of its digits is divisible by 3 a number is divisible by 6 is the sum of its digits is divisible by 3, and the number is even. a number is divisible by 9 if the sum of its digits is divisible by 9. a number is divisible by 11 if the alternating sum of its digits is divisible by a multiple of 11 (so divisible by 0, 11, 22, 33, etc - don't forget the zero, that is also a multiple of 11). for example, the number 2354 is divisible by 11 since 2-3+5-4=0. the number 9680 is divisible by 11 since 9-6+8-0=11 c given that information for what values of a and b is the number 12ab divisible by 99?