Exercice 39 svp niveau 4ème :)

Exercice 39
* signifie multiplié par
a. 1.5/5 = 15/50 = (3*5)/(10*5) = 3/10
b.-2,7 / 3,6 = -27/36 = (-3*9)/(3*12) = -9/12
c. 4,1/-2,5 = 41/-25
d. -1/-0.25 = -100/-25 = (-4*25)/-25 = 4/1
e. -(1.21/7.7) = -(121/770) = -((11*11)/(11*70) = -(11/70)
f. -(-3.5/-14) = -(-35/-140) -(35/(35*4)) = -(1/4)