Bonjour
a. 8/14 + 15/21
= (8 x 3) / (14 x 3) + (15 x 2) / (21 x 2)
= 24/42 + 30/42
= 54/42
= (6 x 9) / (6 x 7)
= 9/7
b. 7/9 - 14/36
= (7 x 4) / (9 x 4) - 14/36
= 28/36 - 14/36
= 14/36
= (2 x 7) / (2x 18)
= 7/18.
c. 15/20 + 14/8
= (15 x 2) / (20 x 2) + (14 x 5) / (8 x 5)
= 30/40 + 70/40
= 100/40
= (20 x 5) / (20 x 2)
= 5/2.
