Đáp án:
Bài 1: Tính
a, `4545/5757 - 151515/191919`
` = 45/57 - 15/19`
` = 15/19 - 15/19 = 0`
b, `17/2 - (3/5 + 9/2)`
`= 17/2 - 3/5 - 9/2`
`= (17/2 - 9/2) - 3/5`
`= 4 - 3/5 = 20/5 - 3/5 = 17/5`
c, `1/2 - (3/4 + -5/6) - 5/6`
`= 1/2 - 3/4 + 5/6 - 5/6`
`= (1/2 - 3/4) + (5/6 - 5/6)`
`=- 1/4`
d, `1/3 - (3/5 + -5/2)+ 3/5`
`= 1/3 - 3/5 + 5/2 + 3/5`
`= (1/3 + 5/2) - (3/5 - 3/5)`
`= 17/6`
Bài 2: Tìm x
a, `x - 1/5 = 3/7`
` x = 3/7 + 1/5`
` x = 22/35`
b, `x + 3/4 = 1/2`
`x = 1/2 - 3/4`
`x = -1/4`
c, `11/12 - (2/5 - x) = 2/3`
`11/12 - 2/5 + x = 2/3`
`31/60 + x = 2/3`
` x = 2/3 - 31/60`
` x = 3/20`
d, `-x + 2/3 = 3/5 - (-1/6)`
` -x + 2/3 = 3/5 + 1/6`
`-x + 2/3 = 23/30`
`-x = 23/30 - 2/3`
`-x = 3/30 = 1/10`
`⇒ x = -1/10`
