4eme devoir de maths pouvez vous m'aider svp?

a. 2/3×1/5 = 2/15
b. -5/7×-1/4 = 5/28
c. 5/6×-11/7 = -55/42
d. 8×8/1 = 8×8 = 64
e. -3/2×7/-5 = -21/-10 = 21/10
f. 1/10×-9/7 =-9/70