Bonsoir
a) 4/7+2/3
= 4 x 3 / 7 x 3 + 2 x 7 / 3 x 7
= 12/21 + 14/21
= 26/21
b) 2/3+1/8
= 2 x 8 / 3 x 8 + 1 x 3 / 8 x 3
= 16/24 + 3/24
= 19/24
c)3/5+2/9
= 3 x 9 / 5 x 9 + 2 x 5 / 9 x 5
= 27/45 + 10/45
= 37/45
d) 2/7-4/5
= 2 x 5 / 7 x 5 - 4 x 7 / 5 x 7
= 10/35 - 28/35
= - 18/35
e) -3/4-5/7
= - 3 x 7 / 4 x 7 - 5 x 4 / 7 x 4
= - 21/28 - 20/28
= - 41/28
f) -5/3+18/7
= - 5 x 7 / 3 x 7 + 18 x 3 / 7 x 3
= - 35/21 + 51/21
= 19/21