8/5 + 18/27 = 216/135 + 90/135
= 306/135
= 34/15
Vậy 8/5 + 18/27 = 34/15
12/20 - 6/18 = 3/5 - 1/3
= 9/15 - 5/15
= 4/15
Vậy 12/20 - 6/18 = 4/15
8/24 x 5/25 = 1/3 x 1/5
= 1/15
Vậy 8/24 x 5/25 = 1/15
18/21 : 12/27 = 18/21 x 27/21
= 6/7 x 9/7
= 54/49
Vậy 18/21 : 12/27 = 54/49