Exercice 2:
A= 2/7 + 3/7 : 5/2
= 2/7 + 3/7 * 2/5
= 2/7 + 6/35
= 2*35 / 7*35 + 6*7/35*7
= 70/245 + 42/245
= 70+42/245
= 112/245
= 16*7 / 7*35
= 16/35
* c'est le signe de multiplication
B= 5*(1/3-3/11)
= 5*(1*11/3*11 - 3*3/11*3)
= 5* (11/33 - 9/33)
= 5*2/33
= 10/33