Bonjour,
a. 2/7 + 4/9
= (2 x 9)/(7 x 9) + (4 x 7)/(9 x 7)
= 18/63 + 28/63
= 46/63
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
= 1/1 + 2/9
= (1 x 9)/(1 x 9) + 2/9
= 9/9 + 2/9
= 11/9
e. 1 - 7/3
= 1/1 - 7/3
= 3/3 - 7/3
= -4/3
f. 3 + 3/4
= 3/1 + 3/4
= (3 x 4)/(1 x 4) + 3/4
= 12/4 + 3/4
= 15/4
