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number theory junior
Problem
The number is a two-digit number. • When is divided by , the remainder is . • When is divided by , the remainder is . What is the remainder when is divided by ?
(A)
(B)
(C)
(D)
(E)
Solution
From the second bullet point, we know that the second digit must be , for a number divisible by ends in zero. Since there is a remainder of when is divided by , the multiple of must end in a for it to have the desired remainder We now look for this one: The number satisfies both conditions. We subtract the biggest multiple of less than to get the remainder. Thus, .
Final answer
E