20 - 10 + 30 + 50 - 10 + 20
= 10 + 30 + 50 - 10 + 20
= 40 + 30 + 50 - 10 + 20
= 70 + 50 - 10 + 20
= 120 - 10 + 20
= 110 + 20
= 130
20 - 10 + 30 + 50 - 10 + 20 =
= 10 + 20 + 50 - 10 + 20
= 30 + 50 - 10 + 20
= 80 - 10 + 20
= 70 + 20
= 90
20-10+30+50-10+20=10+30+50-10+20=40+50-10+20=90-10+20=80+20=100
20 - 10 + 30 + 50 - 10 +20
=10 + 20 + 50 - 10 + 20
=30 +50 - 10 + 20
= 80 - 10 +20
=70 + 20
= 90