Make 10!

For how many positive integers x x does 82 divided by x x have a remainder of 10?


The answer is 5.

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2 solutions

We are looking for positive integers x x such that 82 = n x + 10 82 = nx + 10 for some integer n n , or in modular form, 82 10 ( m o d x ) 82 \equiv 10 \pmod{x} . We are thus looking for x > 10 x \gt 10 such that 72 0 ( m o d x ) 72 \equiv 0 \pmod{x} . Such x x are the positive divisors of 72 72 that exceed 10 10 , which are 12 , 18 , 24 , 36 12, 18, 24, 36 and 72 72 , a total of 5 \boxed{5} numbers.

Syed Hissaan
Jan 21, 2017

> Since we have remainder of 10 so the number we will be dealing upon is 82 10 = > 72 82 - 10 => 72 now we have to make factors of 72 . by prime factorization method we get 12 total factors . Since we only want the number greater than 10 to have a remainder of 10 so we will remove 1 , 2 , 3 , 4 , 6 , 8 , 9 1,2,3,4,6,8,9 , after we had subtracted 7 ( because we only want factors greater than 10 ) our answer implies 12 7 = = > 12-7 ==> 5

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