Question

X+y=100
x-y=80
x×y=?

Answer 1

Consider x+y=100 as 1st equation
and x-y=80 as 2nd equation
add 1st and 2nd equation
you will get
x+y+x-y=100+80
2x=180
x=90
now substitute x value in 1st equation
you will get
90+y=100
y=100-90
y=10
therefore x=90 and y=10