Explications étape par étape:

a. 8/3 ÷ 12/3 = 8/3 × 3/12 = 8/12 = 2/3

b. 18/3 ÷ 9 = 18/3 × 1/9= (9×2)/3 × 1/9 = 2/3

c. 3 ÷ 4/6 = 3 ÷ 2/3 = 3 × 3/2 = 9/2