Bonsoir,
a. 3/7 + 1/2
= (3 x 2) / (7 x 2) + (1 x 7) / (2 x 7)
= 6/14 + 7/14
= 13/14
b. 2/9 + 15/8
= (2 x 8) / (9 x 8) + (15 x 9) / (8 x 9)
= 16/72 + 135/72
= 151/72
c. 9/5 - 12/17
= (9 x 17) / (5 x 17) - (12 x 5) / (17 x 5)
= 153/85 - 60/85
= 93/85
d. 8/7 - 1/6
= (8 x 6) / (7 x 6) - (1 x 7) / (6 x 7)
= 48/42 - 7/42
= 41/42.