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jmc

number theory intermediate

Problem

Let be a positive integer whose only digits are 0s and 1s. If and is an integer, what is the smallest possible value of ?
Solution
Since is divisible by 12, it must be divisible by both 3 and 4. Hence, the sum of its digits is divisible by 3 and its last two digits are divisible by 4. By inspection, we see that must end in 00 and therefore the smallest such is 11100. Calculating, .
Final answer
925