Bonjour
a. 2/7 + 4/9 = (2 x 9) / (7 x 9) + (4 x 7) / (9 x 7) = 18/63 + 28/63 = 36/63 = (9 x 4) / (9 x 7) = 4/7
b. 3/8 - 5/3 = (3 x 3) / (8 x 3) - (5 x 8) / (3 x 8) = 9/24 - 40/24 = - 31/24
c. - 4/5 - 7/9 = (- 4 x 9) / (5 x 9) - (7 x 5) / (9 x 5) = - 36/45 - 35/45 = - 71/45
d. 1 + 2/9 = (1 x 9) / (1 x 9) + 2/9 = 9/9 + 2/9 = 11/9
e. 1 - 7/3 = (1 x 3) / (1 x 3) - 7/3 = 3/3 - 7/3 = - 4/3
f. 3 + 3/4 = (3 x 4) / (1 x 4) + 3/4 = 12/4 + 3/4 = 15/4.
