Tính Nhanh a.(7/11 : 2/5 + 4/11 : 2/5) x 40 % b.Tìm x sao cho : 4/x = 20 x 0,01

`a.`

`(7/11 : 2/5 + 4/11 : 2/5) xx 40 %`

`=[(7/11+4/11):2/5]xx40%`

`=[1:2/5]xx40%`

`=5/2xx40%`

`=5/2xx4/10`

`=1`

`b.`

`4/x = 20 xx 0,01`

`4:x=0,2`

`x=4:0,2`

`x=20`