Bonjour
a. 2/7 + 3/14 - 1/21
= (2 x 6) / (7 x 6) + (3 x 3) / (14 x 3) - (1 x 2) / (21 x 2)
= 12/42 + 9/42 - 2/42
= 19/42.
b. 5/6 - 19/3 + 7/18
= (5 x 3) / (6 x 3) - (19 x 6) / (3 x 6) + 7/18
= 15/18 - 114/18 + 7/18
= - 92/18
= (2 x - 46) / (2 x 9)
= - 46/9
c. 7/4 + 1/16 - 9/2
= (7 x 4) / (4 x 4) + 1/16 - (9 x 2) / (2 x 2)
= 28/16 + 1/16 - 18/16
= 11/16.
