2019 AMC 10B Problem 14
Problem 14 of 25IntermediateNumber TheoryCounting & Probability
The base-ten representation for is where and denote digits that are not given. What is
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Solution
Because is divisible by , its last three digits are zero, so .
Since is divisible by , its digit sum is divisible by . Hence , so is either or .
Divisibility by says the alternating digit sum is divisible by , so . Checking the digit possibilities from these two congruences gives and . Therefore .
Thus, the answer is C .