bài 1 tính bằng cách thuận tiện nhất a, 2/9+1/5+7/9+4/5 b,1/2+3/16+5/12+5/16 bài 2 tìm x a, x nhân 1/2=1/3 b, x : 4/5=5/6 c, 2/9 : x =2/3 giải nhanh g

$\text{Bài tập 1:}$

`a) 2/9+1/5+7/9+4/5.`

`=(2/9+7/9)+(1/5+4/5).`

`=9/9+5/5.` `=1+1.` `=2.`

`b)1/2+3/16+5/12+5/16`

`=1/2+5/12+(3/16+5/16)`

`=1/2+5/12+(3/16+5/16)`

`=1/2+5/12+8/16`

`=1/2+5/12+1/2`

`=(1/2+1/2)+5/12`

`=2/2+5/12`

`=1+5/12`

`=12/12+5/12`

`=17/12`

$\text{Bài tập 2:}$

`a)x×1/2=1/3`

`⇒x=1/3÷1/2`

`⇒x=1/3×2/1`

`⇒x=2/3`

`b)x÷4/5=5/6`

`⇒x=5/6×4/5`

`⇒x=20/30`

`⇒x=2/3`

`c)2/9÷x=2/3`

`⇒x=2/9÷2/3`

`⇒x=2/9×3/2`

`⇒x=6/18`

`⇒x=1/3`