Bonjour,
Exercice 53:
1. Donner un multiple commun à 5 et 7.
5 x 7 = 35
Ce multiple commun est : 35
2. Calculer alors:
a. 13/15 - 11/20
= (13 x 4) / (15 x 4) - (11 x 3) / (20 x 3)
= 42/60 - 33/60
= 9/60
= (3 x 3) / (3 x 20)
= 3/20
b. 13/15 + 3/7
(13 x 7) / (15 x 7) + (3 x 5) / (7 x 5)
= 91/105 + 15/105
= 106/105
Exercice 54:
Calculer en réduisant au même dénominateur.
a. 2/7 + 4/9
= (2 x 9) / (7 x 9) + (4 x 7) / (9 x 7)
= 18/63 + 28/63
= 46/63
b. 3/8 - 5/3
= (3 x 3) / (8 x 3) - (5 x 8) / (3 x 8)
= 9/24 - 15/24
= - 6/24
= (6 x - 1) / (6 x 4)
= - 1/4
c. -4/5-7/9
= (- 4 x 9) / (5 x 9) - (7 x 5) / (9 x 5)
= - 36/45 - 35/45
= - 71/45
d. 1+2/9
= (1 x 9) / (1 x 9) + 2/9
= 9/9 + 2/9
= 11/9
e. 1-7/3
= (1 x 3) / (1 x 3) - 7/3
= 3/3 - 7/3
= - 4/3
f. 3+3/4
= (3 x 4) / (1 x 4) + 3/4
= 12/4 + 3/4
= 15/4.
