`text{Câu 1:}`
`1. a) 2/5+3/5.(-4/9)`
`= 2/5+(-4/15)`
`= 2/15`
`b) 3-(-0,75)^2+(-0,5)^2:2`
`= 3-0,5625+0,25:2`
`= 3-0,5625+0,125`
`= 2,5625`
`2.`
`17,418 ≈ 17,42`
`text{Bài 2:}`
`a) 1/2+x= 1/4`
`x= -1/4`
`b) -0,52:x= -9,36:16,38`
`-0,52:x= -4/7`
` x= 91/100`