Câu 10:

Ta có: $\frac{x}{2}$ = $\frac{y}{3}$ ⇒ x = $\frac{2y}{3}$ 

$\frac{y}{4}$ = $\frac{z}{5}$ ⇒ z = $\frac{5y}{4}$ 

 Mà x +y -z = 10

⇒ $\frac{2y}{3}$ +y - $\frac{5y}{4}$ = 10

⇒ y.($\frac{2}{3}$ +1 - $\frac{5}{4}$) = 10

⇒ y.$\frac{5}{12}$ = 10

⇒ y = 24

⇒ x = $\frac{2.24}{3}$ = 16; z = $\frac{5.24}{4}$ = 30

Vậy x; y; z lần lượt là: 16; 24; 30

Câu 11:

$a) x + \frac{2}{3} = 2^{5} ÷ 2³$

$⇒ x + \frac{2}{3} = 2²$

$⇒ x = 4 - \frac{2}{3}$

$⇒ x = \frac{10}{3}$

$Vậy$ $x = \frac{10}{3}$

$b) \frac{2}{3} + \frac{5}{3}x = \frac{5}{7}$

$⇒ \frac{5}{3}x =\frac{1}{21}$

$⇒ x = \frac{1}{35}$

$Vậy$ $x = \frac{1}{35}$

$c) |x +5| -6 = 9$

$⇒ |x +5| = 15$

$⇒ \left[ \begin{array}{l}x +5=15\\x +5=-15\end{array} \right. ⇒ \left[ \begin{array}{l}x=10\\x=-20\end{array} \right.$

$Vậy$ $x ∈$ {$10; -20$}

$d) \frac{-12}{13}x -5 = 6\frac{1}{13}$

$⇒ \frac{-12}{13}x = \frac{144}{13}$

$⇒ x = -12$

$Vậy$ $x = -12$

Đáp án: