Bài 5 : Tính nhanh

Đáp án:

 `b)`

`\frac{8,1:0,6xx1875+1,5xx625xx9}{105+205+795+895}`

`=\frac{13,5xx1875+13,5xx625}{(105+895)+(205+795)}`

`=\frac{13,5xx(1875+625)}{1000+1000}`

 `=\frac{13,5xx2500}{2000}`

`=\frac{13,5xx25xx10}{20xx10}`

`=\frac{13,5xx5xx5}{4xx5}`

`=\frac{13,5xx5}{4}`

`=\frac{67,5}{4}`

`=16,875`