Bonjour,
1) 5/7+(2/7-5)
= 5/7 + [2/7 - (5 x 7) / (1 x 7)]
= 5/7 + (2/7 + 35/7)
= 5/7 + 35/7
= 42/7
= (7 x 6) / (7 x 1)
= 6
2) 3/4+2×5+1/2
= 3/4 + 10 + 1/2
= 3/4 + (10 x 4) / (1 x 4) + (1 x 2) / (2 x 2)
= 3/4 + 40/4 + 2/4
= 45/4
3)(3/2+2)(5+1/2)
= [3/2 + (2 x 2) / (1 x 2)] x [(5 x 2) / (1 x 2) + 1/2]
= (3/2 + 4/2) x (10/2 + 1/2)
= 7/2 x 11/12
= 77/4
4) 4/5×(5/4+1)-3/10
= 4/5 x [5/4 + (1 x 4) / (1 x 4)] - 3/10
= 4/5 x (5/4 + 4/4) - 3/10
= 4/5 x 9/4 - 3/10
= 36/20 - 3/10
= (2 x 18) / (2 x 10) - 3/10
= 18/10 - 3/10
= 15/10
= (5 x 3) / (5 x 2)
= 3/2.
5) -5/7+-2/7×1/3
= - 5/7 - 2/21
= (- 5 x 3) / (7 x 3) - 2/21
= - 15/21 - 2/21
= - 17/21
6) 8+21×2/3
= 8 + 42/3
= 8 + 14
= 22
7) 7/3-4/3÷2/5
= 7/3 - 4/3 x 5/2
= 7/3 - 20/6
= 7/3 - (2 x 10) / (2 x 3)
= 7/3 - 10/3
= - 3/3
= - 1
8) 2/5+3/5+(1-1/10)
= (2 x 2) / (5 x 2) + (3 x 2) / (5 x 2) + [(1 x 10) / (1 x 10) - 1/10]
= 4/10 + 6/10 + (10/10 - 1/10)
= 10/10 + 9/10
= 19/10.
9) (1/9-3/5)(8/5+7/9)
= [(1 x 5) / (9 x 5) - (3 x 9) / (5 x 9)] [(8 x 9) / (5 x 9) + (7 x 5) / (8 x 5)]
= (5/45 - 27/45) x (72/45 + 35/45)
= - 22/45 x 2 520/45
= - 55 440/2 0254
= (45 x - 1 232) / (45 x 45)
= - 1 232/45.
