Bài 1:
`a)2/15 . 2/5+(-4)/(-30) . 3/5+2/15`
`=2/15 .(2/5+3/5)+4/30`
`=2/15 . 5/5+2/15`
`=2/15+2/15`
`=4/15`
`b)((-1)/2)²+(-12)/14 . 7/5-1,8:(-4)/7`
`=1/4+(-12)/14 . 7/5-9/5 . (-7)/4`
`=1/4+(-6)/5+63/20`
`=5/20+(-24)/20+63/20`
`=44/20`
`=11/5`
Bài 2:
`a)-3/16:(6/7-x)=-5/16`
`6/7-x=(-3/16):(-5/16)`
`6/7-x=(-3/16) . (-16/5)`
`6/7-x=3/5`
`x=6/7-3/5`
`x=30/35-21/35`
`x=9/35`
`b)50%x-(-0,2x)=0,6`
`1/2x+1/5x=3/5`
`(1/2+1/5)x=3/5`
`(5/10+2/10)x=3/5`
`7/10x=3/5`
`x=3/5:7/10`
`x=3/5 . 10/7`
`x=6/7`
`c)1/12 .(2/3+x)²-222/333=(-2)/(-24)`
`1/12 .(2/3+x)²-2/3=1/12`
`1/12 .(2/3+x)²=1/12+2/3`
`1/12 .(2/3+x)²=1/12+8/12`
`1/12 .(2/3+x)²=9/12`
`1/12 .(2/3+x)²=3/4`
`(2/3+x)²=3/4:1/12`
`(2/3+x)²=3/4 . 12`
`(2/3+x)²=9`
`(2/3+x)²=3²`
`⇒`\(\left[ \begin{array}{l}\dfrac{2}{3}+x=3\\\dfrac{2}{3}+x=-3\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}x=3-\dfrac{2}{3}\\x=-3-\dfrac{2}{3}\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}x=\dfrac{9}{3}-\dfrac{2}{3}\\x=-\dfrac{9}{3}-\dfrac{2}{3}\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}x=\dfrac{7}{3}\\x=-\dfrac{11}{3}\end{array} \right.\)
Bài 3:
`text{Quãng đường từ nhà đến nơi làm việc là:}`
`36. 1/2=18(km``/``h)`
`text{Thời gian bác An đi từ nơi làm việc về nhà là:}`
`18:40=0,45(giờ)`
Đổi `text{0,45 giờ=27 phút}`
Đáp số: `27` `phút`
