Bonjour, je suis en 4ème, j'ai beau essayé se devoirs mais je n'y arrive pas, quelqu'un pourrait m'aider svp Il faut détailler des fractions : A/ 21/8 - 5/8 × 3

Bonsoir
A = 21/8 -5/8 X 3/10
A = 21/8 -15/80
A = 210/80 -15/80
A = 195/80
A = 39/16 

B= 1/2 +9/10 X 5/21
B = 1/2 +45/210
B = 105/210 + 45/210
B = 150/210 = 15/21 = 5/7

C = 15/4 +5/12 / 10/9
C = 15/4 +5/12 X 9/10
C = 15/4 +45/120 
C = 450/120 + 45/120
C = 495/120 = 99/24 = 33/8

D = 5 X 9/10 -7/10
D = 45/10 -7/10
D = 38/10

Bonsoir,

A = 21/8 - 5/8 × 3/10
A = 21/8 - 5/10 x 3/8
A = 21/8 - 1/2 x 3/8
A = 21/8 - 3/16
A = (21 x 2)/(8 x 2) - 3/16
A = 42/16 - 3/16
A = 39/16

B = 1/2 + 9/10×5/21
B = 1/2 + 9/21 x 5/10
B = 1/2 + (3x3)/(3x7) x 1/2
B = 1/2 + 3/7 x 1/2
B = 1/2 + 3/14
B = (1 x 7)/(2x7) + 3/14
B = 7/14 + 3/14
B = 10/14
B = (2x5)/(2x7)
B = 5/7

C = 15/4 + 5/12 : 10/9
C = 15/4 + 5/12 x 9/10
C = 15/4 + 5/10 x 9/12
C = 15/4 + 1/2 x 3/4
C = 30/8 + 3/8
C = 33/8

D = 5× 9/10 - 7/10
D = 45/10 - 7/10
D = 38/10