Réponse :
a/ 1/2 + 1/4 + 3/4 = 1x2/ 2x2 + 1 /4 + 3 /4 = 2/4 + 1/4+3/4 = 6/4 = 3/2
b/ 1/3 +2/3 = 1+2 / 3 = 3/3 = 1
c/ 1/2 +1/3+1/4+2/3+3/4 = 1x6/2x6 + 1x4/3x4 +1x3/4x3 + 2x4/3x4 +3x3/4x3 = 6/12+4/12 + 3/12 + 8/12+9/12 = 30/12
