bjr

ex 1 )

A = 2/3 + 5/3 * 1/15 = 2/3 + 1/9 = 6/9 + 1/9 = 7/9

B = (1-3/7) ÷12/5 = ( 4/7) * 5/12 = 5/21

C = 9/2/3 = 9/2 * 1/3 = 9/6 = 3/2

ex 2)

A = 2/5 + 1 = 2/5 + 5/5 = 7/5

ex 3)

A = 5 - 2/3 -5/6 = 30/6 - 4/6 - 5/6 = 21/6 = 7/2

B = 5/2 - 15/6 *21/25

à toi de la faire

priorité à la multiplication ; )