2.5x+[(249.5-242)-x]x5=252.5x+[(249.5-242)-x]x5=25
2.5x+[(249.5-242)-x]x5=252.5x+[(249.5-242)-x]×5=25两边除以50.5x+7.5-x=5x-0.5x=7.5-50.5x=2.5x=2.5÷0.5x=5
x=5