a) 3,5x + 2,5x = 120
6x = 120
x = 120 : 6
x = 20
b) [46 + 2 * (48 - 45)] * [72 - 2 * (30 - 7)] =
[46 + 2 * 3] * [72 - 2 * 21] =
[46 + 6] * [72 - 42] =
52 * 30 =
1560
c) x/4 + 10 = 20, aducem la acelasi numitor
x + 40 = 80
x = 80 - 40
x = 40
d) a + b = 69
a : b = 10 rest 3
a = 10b + 3
10b + 3 + b = 69
11b = 69 - 3
b = 66 : 11
b = 6
a = 69 - 6
a = 63