15 ⋅ 10 + (30 - 20) ⋅ 5 = 150 + 10 ⋅ 5 = 150 + 50 = 200
15 ⋅ 10 + 30 - 20 ⋅ 5 = 150 + 30 - 100 = 180 - 100 = 80
(120 + 320 : 4) ⋅ 2 = (120 + 80) ⋅ 2 = 200 ⋅ 2 = 400
(120 + 320) : (4 ⋅ 2) = 440 : 8 = 55