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jmc

algebra intermediate

Problem

The product of two positive integers plus their sum is 95. The integers are relatively prime, and each is less than 20. What is the sum of the two integers?
Solution
Let our numbers be and with Then . With Simon's Favorite Factoring Trick in mind, we add to both sides and get , which factors as . We consider pairs of factors of : . Since , we can rule out the first 4 pairs. The pair gives us which doesn't work because and are relatively prime, so we are left with the last pair, which gives and , so .
Final answer
18