65 + (53 - 21) = 65 + 32 = 97
(500 + 100) - 200 = 600 - 200 = 400
(65 - 21) + (24 + 2) = 44 + 26 = 70
1 000 - (600 - 100) = 1 000 - 500 = 500
(16 + 12) + 40 = 28 + 40 = 68
4x+y=3
6x-2y=1 /2
4x+y=3
2x-y=1/2
6x=3+1/2
6x=6/2+1/2
6x=7/2
x=7/2 : 6
x=7/12
6218-1248=4970 7/10 от 4970= 4970:10*7=3479