Question

if x and y are two 3 digit numbers such that x+y = 220 and difference between x and y if 20 then find the number

Answer 1

x+y=220
x-y=20
2x=240
x=120
y=100

Answer 2

x+y=220 -------- 1
x-y=20 ---------2

equation 1+2
2x=240
x = 120
substituting x in 1
120+y=220
y=220-120
=100