Find the number of positive integers with three not necessarily distinct digits, , with .such that both and are multiples of .
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For a b c to be divisible by 4 we require only that b c be divisible by 4 . Allowing for b = 0 there are 2 5 such two-digit "constructs", 5 of which have c = 0 , (namely 0 0 , 2 0 , 4 0 , 6 0 and 8 0 ), leaving us with 2 0 allowable constructs b c .
Then for c b a to also be divisible by 4 we require that b a be divisible by 4 . For each of the previous 2 0 constructs b c there will be 2 corresponding constructs b a that will be divisible by 4 such that a = 0 , (i.e., 2 for each value of b from 0 through 9 ), giving us a total of 2 × 2 0 = 4 0 desired integers.