Problem Solving

If x and y are positive integers and 1+x+y+xy=15, what is the value of x+y?



answer: 6

likewhoa wrote:If x and y are positive integers and 1+x+y+xy=15, what is the value of x+y?

answer: 6

What i did to solve this problem was a simple exercise of trial and error.

One has the following equation: x+y+x*y = 14

Because the sum of three integers is even, you know that either x, y and xy are even or two are odd and the third is even. This last option is not possible, because if X and Y are odd, xy is also odd.

Let's try with 2 and 4: 2+4+2*4= 14, so X+Y = 6