If x and y are positive integers for which 3x + y + xy = 115, then what is x + y?
3x + y + xy = 115 ---> y + xy = 15 - 3x ---> y(1 + x) = 15 - 3x ---> y = (15 - 3x) / (1 + x)
Graphing this, I get the point (1, 56).
From this, we can get the value of x + y.
Oops!
Electric Pavlov found that I switch the 115 to only 15; so the equation should be: y = (115 -3x) / (1 + x).
However, the point remains the same.
