a/ 3 1 3 - 1 3 4 = 10 3 - 7 4 = 40 12 - 21 12 = 40 - 21 12 = 19 12
b/ 2 5 6 + 1 2 3 = 17 6 + 5 3 = 17 6 + 10 6 = 17 + 10 6 = 27 6 = 9 2
c/ 2 3 8 : 1 3 4 = 19 8 : 7 4 = 19 8 × 4 7 = 19 × 4 8 × 7 = 76 56 = 19 14
d/ 1 3 7 x 1 5 8 = 10 7 × 13 8 = 10 × 13 7 × 8 = 130 56 = 65 28