A
x=80*9/6
x=120
b
x-273=786-129
x=675+273=948
c
34x=260+12
x=272/34
x=8
d
x+317=2400/3
x=800-317
x=483
1 способ:
30 * 2 + 6 * 2 = 60 + 12 = 72
2 способ:
30 * 2 + 6 * 2 = (30 + 6) * 2 = 36 * 2 = 72
Всё просто!!!
7/8 - 3/4 = 7/8 - 6/8 = 1/8
7/10 + 3/5 - 4/5 = 14/20 + 12/20 - 16/20 = 10/20 = 1/2