If p, q, r are positive integers such that p+1q+1r=2519, then find q.
Since p, q, and r must all be positive, p=1 because if it was any higher, q and r would need to be negative to make equation true. So we have 1+1q+1r=2519. So 1q+1r=619=66q+6r, so 19=6q+6r. The only possibility of q is 3, with r being 6.