bonjour j'espère que ça va voilà les réponses :
13/20 - 20/7 =-7/7 = -1
-5/4+2/3 = -15/12 + 8/12 = -7/12
1/6 - 5/3 = 1/6 - 10/6= -9/6 = -3/2
-5/3×2/7 = -10/21
12/-5 × -15/8 = 2×6×3×5/-1×5×2×4 = 18 /-4= 9/-2
2/9÷-7/5= 2/9×5/7= 10/63
-5/14÷-10/-21= -5/14× -21/-10 = -1×5×-3×7/2×7×-2×5= 3/-4
a barrer