Câu 23:
a: \(\left(-12,5\right)+17,55+\left(-3,5\right)-\left(-2,45\right)\)
\(=\left(-12,5-3,5\right)+\left(17,55+2,45\right)\)
\(=20-16=4\)
b: \(-\dfrac{3}{7}\cdot\dfrac{15}{13}-\dfrac{3}{7}\cdot\dfrac{11}{13}-\dfrac{3}{7}\)
\(=-\dfrac{3}{7}\left(\dfrac{15}{13}+\dfrac{11}{13}+1\right)\)
\(=-\dfrac{3}{7}\left(2+1\right)=-\dfrac{3}{7}\cdot3=-\dfrac{9}{7}\)
Câu 24:
a: x+3,12=14,6-8,5
=>x+3,12=6,1
=>x=6,1-3,12=2,98
b: \(\dfrac{x}{2}=\dfrac{8}{-4}\)
=>\(\dfrac{x}{2}=-2\)
=>\(x=-2\cdot2=-4\)
c: \(\dfrac{17}{5}:x-\dfrac{3}{5}=-\dfrac{1}{5}\)
=>\(\dfrac{17}{5}:x=-\dfrac{1}{5}+\dfrac{3}{5}=\dfrac{2}{5}\)
=>\(x=\dfrac{17}{5}:\dfrac{2}{5}=\dfrac{17}{2}\)
CÂU 23:
\(a;\left(-12,5\right)+17,55+\left(-3,5\right)-\left(-2,45\right)\\ =\left[\left(-12,5\right)+\left(-3,5\right)\right]+\left[17,55-\left(-2,45\right)\right]\\ =-16+20=4\\ b;\dfrac{-3}{7}\cdot\dfrac{15}{13}-\dfrac{3}{7}\cdot\dfrac{11}{13}-\dfrac{3}{7}\\ =\dfrac{-3}{7}\cdot\left(\dfrac{15}{13}+\dfrac{11}{13}+1\right)\\ =-\dfrac{3}{7}\cdot3=-\dfrac{9}{7}\)
CÂU 24:
\(a;x+3,12=14,6-8,5\\ x=14,6-8,5-3,12\\ x=2,98\\ b;\dfrac{x}{2}=\dfrac{8}{-4}\\ x=\dfrac{2\cdot8}{-4}=-4\\ c;\dfrac{17}{5}:x-\dfrac{3}{5}=-\dfrac{1}{5}\\ \dfrac{17}{5}:x=\dfrac{2}{5}\\ x=\dfrac{17}{5}:\dfrac{2}{5}\\ x=\dfrac{17}{2}\)
