Bonjour,
a) 5,4/9 + 11,2/27
= (5,4 x 3) / (9 x 3) + 11,2/27
= 16,2/27 + 11,2/27
= 27,4/27
= (27,4 x 10) / (27 x 10)
= 274/270
= (2 x 137) / (2 x 135)
= 137/135
b) 23/18 - 2,1/6
= 23/18 - (2,1 x 3) / (6 x 3)
= 23/18 - 6,3/18
= 16,7/18
= (16,7 x 10) / (18 x 10)
= 167/180
c) 3/1,1 - 3/11
= (3 x 100) / (1,1 x 100) - (3 x 10) / (11 x 10)
= 300/110 - 30/110
= 270/110
= (10 x 27) / (10 x 11)
= 27/11
d) 1/2,5 + 1/7,5
= (1 x 30) / (2,5 x 30) + (1 x 10) / (75 x 10)
= 30/75 + 10/75
= 40/75
= (5 x 8) / (5 x 15)
= 8/15.
