Bài 1: Tính giá trị của các biểu thức sau:
a) \(\frac{5}{23} \frac{17}{26} + \frac{5}{23} \frac{9}{26}\)
b) \((15,25 + 3,75) \cdot 4 + (20,71 + 5,29) \cdot 5\)
c) \(25\% - \frac{1}{2} + 0,5 \cdot \frac{12}{5}\)
Bài 2: Tìm x, biết:
a) \(\frac{4}{5} + \frac{7}{6} \cdot x = \frac{1}{6}\)
b) \(\frac{2}{9} \cdot \frac{7}{8} \cdot x = 1\)
c) \(\frac{x - 2}{3} = \frac{x + 1}{4}\)
bài 1:
\(a;\dfrac{5}{23}+\dfrac{17}{26}+\dfrac{5}{23}\cdot\dfrac{9}{26}\\ =\dfrac{5}{23}\cdot\left(\dfrac{17}{26}+\dfrac{9}{26}\right)\\ =\dfrac{5}{23}\cdot\dfrac{26}{26}=\dfrac{5}{23}\cdot1=\dfrac{5}{23}\\ b;\left(15,25+3,75\right)\cdot4+\left(20.71+5,29\right)\cdot5\\ =19\cdot4+26\cdot5=76+130=206\\ c;25\%-1\dfrac{1}{2}+0,5\cdot\dfrac{12}{5}\\ =\dfrac{1}{4}-\dfrac{3}{2}+\dfrac{1}{2}\cdot\dfrac{12}{5}=\dfrac{1}{4}-\dfrac{3}{2}+\dfrac{6}{5}\\ =\dfrac{5}{20}-\dfrac{30}{20}+\dfrac{24}{20}=-\dfrac{1}{20}\)
bài 2:
\(a;\dfrac{4}{5}+\dfrac{7}{6}:x=\dfrac{1}{6}\\ \dfrac{7}{6}:x=\dfrac{1}{6}-\dfrac{4}{5}\\ \dfrac{7}{6}:x=-\dfrac{19}{30}\\ x=\dfrac{7}{6}:\left(-\dfrac{19}{30}\right)\\ x=\dfrac{7}{6}\cdot\left(-\dfrac{30}{19}\right)=-\dfrac{35}{19}\\ b;\dfrac{2}{9}-\dfrac{7}{8}\cdot x=1\\ \dfrac{7}{8}\cdot x=\dfrac{2}{9}-1\\ \dfrac{7}{8}\cdot x=-\dfrac{7}{9}\\ x=-\dfrac{7}{9}:\dfrac{7}{8}\\ x=-\dfrac{7}{9}\cdot\dfrac{8}{7}=-\dfrac{8}{9}\\ c;\dfrac{x-2}{3}=\dfrac{x+1}{4}\\ ⇒\: 4\cdot\left(x-2\right)=3\cdot\left(x+1\right)\\ ⇒\: 4x-8=3x+3\\ ⇒\: 4x-3x=3+8\\ ⇒\: x=11\)
