Réponse :
Explications étape par étape :
1)
30/8 x 24/7
= (30 x 24) / (8 x 7)
= (30 x 3 x 8) / (8 x 7)
= (30 x 3) / 7
= 90 / 7
2)
9/5 x 60/21
= (9 x 60) / (5 x 21)
= (3 x 3 x 12 x 5) / (5 x 3 x 7)
= (3 x 12) / 7
= 36/7
3)
120/15 : 80/25
= 120/15 x 25/80
= (120 x 25) / (15 x 80)
= (10 x 4 x 3 x 5 x 5) / (5 x 3 x 10 x 4 x 2)
= 5/2