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Printsmc
number theory senior
Problem
Let be a -digit number, and let and be the quotient and the remainder, respectively, when is divided by . For how many values of is divisible by ?
(A)
(B)
(C)
(D)
Solution
When a -digit number is divided by , the first digits become the quotient, , and the last digits become the remainder, . Therefore, can be any integer from to inclusive, and can be any integer from to inclusive. For each of the possible values of , there are at least possible values of such that . Since there is "extra" possible value of that is congruent to , each of the values of that are congruent to have more possible value of such that . Therefore, the number of possible values of such that is .
Final answer
B