x : 7 : 2 : 5 = 8
x = 8 × 5 × 2 × 7 → metoda mersului invers
x = ( 8 × 7 ) × ( 5 × 2) → inmultirea este asociativa
x = 56 × 10
x = 560
Verific: 560 : 7 : 2 : 5 = 80 : 2 : 5 = 40 : 5 = 8
x : 3 : 9 : 9 = 1
x = 1 × 9 × 9 × 3 → metoda mersului invers
x = 9 × 9 × 3
x = 81 × 3
x = 243
x × 2 × 3 × 5 = 780
x = 780 : 5 : 3 : 2
x = 156 : 3 : 2
x = 52 : 2
x = 26
x : 5 × 6 : 2 = 450
x = 450 × 2 : 6 × 5
x = 900 : 6 × 5
x = 150 × 5
x = 750
Verific: 750 : 5 × 6 : 2 = 150 × 6 : 2 = 900 : 2 = 450
7 x a - 35 x 12 = 378
7 × a - 420 = 378
7 × a = 378 + 420
a = 798 : 7
a = 114
945 : a + 63 x 20 = 1 269
945 : a + 1 260 = 1 269
945 : a = 1 269 - 1 260
945 : a = 9
a = 945 : 9
a = 105
