Répondre :
Bonjour,
Equations :
1) 5 :7 x = 3:4
5/7 x = 3/4
x = 3/4 * 7/5
x = 21/20
2) 2,4:3,5x=8:15
2,4/3,5 x = 8/15
24/35 x = 8/15
x = 8/15 * 35/24
x = 35/15 * 8/24
x = (7*5)/(3*5) * 8/(3*8)
x = 7/3 * 1/3
x = 7/9
3)5:8x=40
5/8 x = 40
x = 40 * 8/5
x = 64