Câu `21` :
`(-5)/11 . 4/13+(-5)/11 . 9/13`
`=(-5)/11(9/13+4/13)`
`=(-5)/11 . 1`
`=(-5)/11`
`=>` Chọn đáp án `B `
Câu `22` :
`6/7 + 5/8:5 - 3/16 . (-2)^2`
`=6/7+5/8 . 1/5 - 3/16 . 4`
`=6/7+1/8-3/16 . 4`
`=55/56-3/4`
`=13/56`
`=>` Chọn đáp án `A`
Câu `23` :
`15/x =(-3)/4`
`=>((-3).(-5))/x=(-3)/4`
`=>((-3).(-5))/x=((-3.(-5))/(4.(-5))`
`=>x=4.(-5)`
`=>x=(-20)`
`=>` Chọn đáp án `C`
Câu `24` :
`|x+2/5|=1/2`
`=>` \(\left[ \begin{array}{l}x+\dfrac{2}{5}=-\dfrac{1}{2}\\x+\dfrac{2}{5}=\dfrac{1}{2}\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=-\dfrac{9}{10}\\x=\dfrac{1}{2}-\dfrac{2}{5}\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=-\dfrac{9}{10}\\x=\dfrac{1}{10}\end{array} \right.\)
Vậy `x=(-9/10;1/10)`
`=>` Chọn đáp án `B`
