Réponse:
Bonjour,
Explications étape par étape:
a. 3/5 = 3×7 / 5×7 = 21/35
3×7 = 21
5×7 = 35
b. 3/4 = 3×15 / 4×15 = 45/60
3×15 = 45
4×15 = 60
c. 80/100 = 80÷20 / 100÷20 = 4/5
80÷20 = 4
100÷20 = 5
d. 49/21 = 49÷7 / 21÷7 = 7/3
21÷3 = 7
donc 49÷7 = 7
21÷7 = 3
Voilà
