a, 360 – 98 = (360 + 2) – (98 + 2) = 362 – 100 = 262

2773 – 995 = (2773 + 5) – (995 + 5) = 2778 – 1000 = 1778

b, 250.36 = (250.4).(36:4) = 1000.9 = 9000

500.12 = (500.2).(12:2) = 1000.6 = 6000

c, 1200 : 50 = (1200.2):(50.2) = 2400 : 100 = 24

9000 : 250 = (9000.4):(250.4) = 36000:1000 = 36

d, 162:9 = (90:9) + (72:9) = 10 + 8 = 18

432 : 4 = (400:4) + (32:4) = 100 + 8 = 108

a) 52 – 42 + 37 – 28 + 38 + 63 = (52 – 42) + (37 + 63) + (38 – 28) = 10 + 100 + 10 =  120

b) 130 + 35.19 – 9.70 – 30

= (35.19 – 9.70) + (130 – 30) = (35.19 – 9.35.2) + 100 = 35.(19 – 18) + 100 = 35 + 100 = 135

c) (11 + 13 + 15 + … + 19).(6.8 – 48) = (11+13+15+…+19).0 = 0

d) (72 – 8.9):(20+22+24 – 19 +21+23) = 0:(20+22+24 – 19 +21+23) = 0

a) 477.1993 – 1993.467 = 1993(477 – 467) = 1993.10 = 19930

b) 38 + 38.22 – 38.10 – 38.3 = 38.(1 + 22 – 10 – 3) = 38.10 = 380

c) (357.45 + 74.357):119 = [357.(45+74)]:119 = 357.119 : 119 = 357

a) 252525.4 – 999999 = 25.10101.4 – 99.10101 = 10101.(100 – 99) = 10101

b) 250025.4 – 500050.2 = 25.4.10001 – 50.2.10001 = 100.10001 – 100.10001 = 0

a) 42.50 – 38.50 – 25.4 = 50.(42 – 38) – 25.4 = 50.4 – 25.4 = (50 – 25).4 = 25.4 = 100

b) 32.38 + 17.94 – 15.38 – 32.17 = 38.(32 – 15) + (94 – 32).17 = 38.17 + 62.17 = 17.(38+62) = 17.100 = 1700

a) 814 – (x – 305) = 712

x – 305  = 102

x = 407

b) 11x – 35 = 108

11x = 143

x = 13

c) 12.(x + 37) = 504

x + 37 = 42

x = 5

d) (7x – 15) : 3 = 2

7x - 15 = 6

7x = 21

x = 3

a) x : [(1800 + 600):30] = 560 : (315 – 35)

x : 80 = 2

x = 160

b) [(250 – 25):15] : x = (450 – 60) : 130

15:x=3

x = 15:3

x = 5

c) [(6x – 72) : 2 – 84].28 = 5628

(6x – 72) : 2 – 84=201

(6x – 72) : 2 = 285

6x -72 = 570

x = 107

d) 5x + x – 6 = 12

6x - 6 = 12

6x = 18

x = 3