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Integer Division (Posted on 2024-09-09) Difficulty: 2 of 5
For how many integers n is n/(100-n) also an integer?

No Solution Yet Submitted by Danish Ahmed Khan    
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Solution Solution Comment 2 of 2 |
Let m be the resultant integer.  Then n/(100-n) = m.
Cross multiply and rearrange the terms: mn - 100m + n = 0
Subtract 100 from each side and factor: (m+1)*(n-100) = -100

So now I can conclude that there is an integer solution for each of the signed factorizationss of -100.  100=2^2+5^2, so the number of factorizations is 2*(2+1)*(2+1)=18.

The 18 values of n can be derived by taking any signed factor of -100 and adding 100 to that factor.

Edited on September 9, 2024, 1:26 pm
  Posted by Brian Smith on 2024-09-09 13:23:22

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