4.
а) (2x + 4) × 20 - 85 = 35,
40x + 80 - 85 = 35,
40x - 5 = 35,
40x = 35 + 5,
40x = 40,
x = 40 : 40,
x = 1
б) 18 + ((82 - 10x) : 6) = 20,
18 + (2(41 - 5x) : 6) = 20,
18 + ((41-5x) : 3) = 20,
54 + 41 - 5x = 60,
95 - 5x = 60,
-5x = 60 - 95,
-5x = -35,
x = (-35) : (-5),
x = 7,
Ответ: а) 1, б) 7.
5.
а) 12 × (32 - (36 + 8x) : 5) = 144,
32 - ((36 + 8x) : 5) = 12,
160 - (36 + 8x) = 60,
160 - 36 - 8x = 60,
124 - 8x = 60,
-8x = 60 - 124,
- 8x = -64,
x = (-64) : (-8),
x = 8.
б) 10 : ((8x + 24) : 5 : 4 + 6) = 1,
10 : ((2x + 6 + 30) : 5) = 1,
10 × (5 : (2x + 36)) = 1,
25 : x + 18 = 1,
25 = x + 18,
- x = 18 - 25,
- x = - 7,
x = 7.
Ответ: a) 8, б) 7.