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December 13, 2019 at 8:14 pm
#975

Pratham S.

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Question 2: We have the given equation. To keep our life easier, we would cancel out the 7. The best way to do that would be to assume one of the numbers say r, is equal to 7. Then we get pq = p + q + 7. We want to now factor this. You get pq – p – q = 7. Turn that into -pq + p + q = 7. Then you get that (p-1)(q-1) -1 = 7, so (p-1)(q-1) = 8. The values of p and q have o be 3 and 5. So, p + q + r = 7 + 3 + 5(all are primes) = **15**.