Bài 6 :
2/5 + 3/4 = 23/20
7/12 - 2/7 + 1/12 = 8/21
12/17 - 5/17 - 4/17 = 3/17
675,39 + 342,14 =1017,53
563,87 + 403, 13 - 328,35 = 638,65
Bài 7:
a, 7/11 + 3/4 + 4/11 + 1/4 = ( 7/11 + 4/11) + ( 3/4 + 1/4 ) = 1 + 1 = 2
b, 72/99 - 28/99- 14/99 = 72/99 - ( 28/99 + 14/99 ) = 72/99 - 42/99 = 30/99
c, 69,78 + 35,97 + 30,22 = ( 69,78 + 30,22 ) + 35,97 = 100 + 35,97 =135,97
d, 83,45 - 30,98 - 42,47 = 83,45 - ( 30,98 + 42,47 ) = 83,45 - 73,45 = 10