Bài 3:
Số công nhân còn lại là: 20-8=12(người)
Thời gian hoàn thành sẽ là:
\(20\cdot\dfrac{60}{12}=100\left(ngày\right)\)
Bài 2:
a: \(\dfrac{x}{-2,5}=\dfrac{4}{5}\)
=>\(x=\dfrac{4}{5}\cdot\left(-2,5\right)=-\dfrac{10}{5}=-2\)
b: \(\dfrac{5}{6}-\dfrac{23}{12}x=\left(-\dfrac{1}{2}\right)^3\)
=>\(\dfrac{5}{6}-\dfrac{23}{12}x=-\dfrac{1}{8}\)
=>\(\dfrac{23}{12}x=\dfrac{5}{6}+\dfrac{1}{8}=\dfrac{20+3}{24}=\dfrac{23}{24}\)
=>\(x=\dfrac{23}{24}:\dfrac{23}{12}=\dfrac{23}{24}\cdot\dfrac{12}{23}=\dfrac{12}{24}=\dfrac{1}{2}\)
Bài 1:
a: \(\dfrac{3}{5}+\dfrac{-1}{2}=\dfrac{6}{10}+\dfrac{-5}{10}=\dfrac{6-5}{10}=\dfrac{1}{10}\)
b: \(\dfrac{1}{2}\cdot\sqrt{16}+\sqrt{\dfrac{9}{16}}+\sqrt{144}\)
\(=\dfrac{1}{2}\cdot4+\dfrac{3}{4}+12\)
\(=2+12+\dfrac{3}{4}=14,75\)
c: \(25\cdot\left(-\dfrac{1}{5}\right)^2+\dfrac{1}{5}-2\cdot\left(-\dfrac{1}{2}\right)^2-\dfrac{1}{2}\)
\(=25\cdot\dfrac{1}{25}+\dfrac{1}{5}-2\cdot\dfrac{1}{4}-\dfrac{1}{2}\)
\(=1+\dfrac{1}{5}-\dfrac{1}{2}-\dfrac{1}{2}=\dfrac{1}{5}\)
