A = 9/5 + 2/5 * 11/4 B = 8/3 - 8/3 * 9/16 C = 8/3 - 5/7 : 20/21 D = 1/7 + 6/5 : 12/35

Faire les multiplications et les divisions d'abord.
A = 9/5 + 2/5 × 11/4
   = 9/5 + 2×11/5×4
   = 9/5 + 22/20
   = 9×4/5×4 + 22/20
   = 36/20 + 22/20
   = 58/20
   = 29/10

B = 8/3 - 8/3 × 9/16
    = 8/3 - 8×9/3×16
    = 8/3 - 72/48
    = 8×16/3×16 - 72/48
    = 128/48 - 72/16
    = 56/16
    = 7/2

C =  8/3 - 5/7 ÷ 20/21 
    = 8/3 - 5/7 × 21/21
    = 8/3 - 5×21/7×20
    = 8/3 - 105/140
    = 8/3 - 3/4
    = 8×4/3×4 - 3×3/4×3
    = 32/12 - 9/12
    = 23/12

D = 1/7 + 6/5 ÷ 12/35
    = 1/7 + 6/5 × 35/12
    = 1/7 + 6×35/5×12
    = 1/7 + 210/60
    = 1×60/7×60 + 210×7/60×7
    = 60/420 + 1 470/420
    = 1 530/420
    = 1 530÷30/420÷30
    = 51/14