Use an equation for questions like these: I'll use x and y as the unknown numbers x-y=0.7 x+y=1 Just choose either x or y to solve for y=x-0.7 y=-x+1 Then since since they're both equal to y then they can equal each other x-0.7=-x+1 2x-0.7=1 2x=1.7 x=0.85 Then just grab one of the equations and use it to find y 0.85+y=1 y=0.15