pouvez-vous m'aider pour l'exercice 1?

1)
5/7 x 21 = 105/21 = 5

2)
4,5 x 10/3 = 45/3 = 15
3,2 x 9/5 = 28,8/5 = 5,76

3)
6,25/4,1 = 6,25 x 100 / 4,1 x 100 = 625/410

4)
240 x 3/4 = 720/4 = 180 litres d'eau

5)
- 2/3 + 5/6 = - 2 x 2 / 3 x 2 + 5/6 = - 4/6 + 5/6 = 1/6
3/2 - 1/5 = 3 x 5 / 2 x 5 - 1 x 2 / 5 x 2 = 15/10 - 2/10 = 13/10
- 3/4 : 2/7 = - 3/4 x 7/2 = - 21/8

6)
12/10 = 2 x 6 / 2 x 5 = 6/5
- 55/33 = 11 x - 5 / 11 x 3 = - 5/3
8/6 = 2 x 4 / 2 x 3 = 4/3

7)
3/4 = 3 x 6 / 4 x 6 = 18/24 h
5/6 = 5 x 4 / 6 x 4 = 20/24 h
1/12 = 1 x 2 / 12 x 2 = 2/24 h
3/2 = 3 x 12 / 2 x 2 = 36/24 h

Donc :
1/12 h < 3/4 h < 5/6 h < 3/2 h

8)
3/5 + 4/5 = 7/5

9)
a) 25/4 = 6 + 25/100
b) 22/7 = 3 + 14/100
c) 355/113 = 3 + 14/100