If X+y=153 and x/y=0.7 then what is x-y
we have x/y = 0.7
i.e. x/y = 7/10
or, 10x = 7y
Now we have
x + y = 153 (multiply everything by 10)
10x + 10y = 1530 (now substitute for 10x = 7y)
7y + 10y = 1530
17y = 1530
y = 1530/17 = 90
y = 90
x = 153 - 90 = 63
x = 63
x - y = 63 - 90 = -27
x - y = -27