Question

Mark (✓) against the correct answer
If x : y = 3 : 4, then (7x + 3y) : (7x − 3y) = ?

(a) 4 : 3
(b) 5 : 2
(c) 11 : 3
(d) 37 : 39

Answer 1

$\frac{x}{y}=\frac{3}{4}$

$$\begin{gathered} x=\frac{3y}{4} \\ \therefore \frac{7x+3y}{7x-3y}=\frac{7{\displaystyle \frac{3y}{4}}+3y}{7{\displaystyle \frac{3y}{4}}-3y} \\ =\frac{21y+12y}{21y-12y}=\frac{33y}{9y}=\frac{11}{3} \end{gathered}$$

Hence, (7x + 3y) : (7x − 3y) = 11 : 3

The correct option is (c).