1) a) 4/7 - 9/7 = -2/7
b) 8/5 - 11/5 = (8 - 11)/5 = -3/5
-11/7 + 5/7 = (-11 + 7)/5 = -4/7
-3/4 + (-5/4) = (-3 + -5)/4 = -8/4 = -2
2) a) Multiple de 3 : 3, 6, 9, 12, 15
Multiple de 5 : 5, 10, 15
b) 2/3 = (2×5)/(3×5) = 10/15
3/5 = (3×3)/(5×3) = 9/15
c) Elle a obtenu (10+9)/15 = 19/15 de cocktail
d) 2L = 30/15
30/15 - 19/15 = (30 - 19)/15 = 11/15
Elle doit ajouter 11/15 L de limonade.
Voilà ! :)