x+y=20 x-y=10 3x+y=50 2x-y=20

x+y=20 x-y=10 x=20-y 20-y-y=10 x=20-y -2y=-10 /:(-2) x=20-y y=5 x=20-5 y=5 x=15 y=5 b). 3x+y=50 2x-y=20 y=50-3x 2x-50+3x=20 y=50-3x 5x=70 /:5 y=50-3x x=14 y=8 x=14

x+y=20 x-y=10 x=20-y 20-y-y=10 x=20-y 20-2y=10 x=20-y -2y=-10 |:-2 x=20-y y=5 x=20-5 x=15 3x+y=50 2x-y=20 y=50-3x 2x-(50-3x)=20 y=50-3x 2x-50+3x=20 y=50-3x 5x=70 |:5 y=50-3x x=14 y=50-3*14 y=50-42=8