Ratio and Proportion — MATHS STD 7 — Question

2. 20 : 15 : 12

Solution:

As, $\text{a}:\text{b}=5:7$ and $\text{b}:\text{c}=6:11$

$\Rightarrow\frac{\text{a}}{\text{b}}=\frac57$ and $\frac{\text{b}}{\text{c}}=\frac{6}{11}$

$\Rightarrow\frac{\text{a}}{\text{b}}=\frac{5\times6}{7\times6}$ and $\frac{\text{b}}{\text{c}}=\frac{6\times7}{11\times7}$

$\Rightarrow\frac{\text{a}}{\text{b}}=\frac{30}{42}$ and $\frac{\text{b}}{\text{c}}=\frac{42}{77}$

$\Rightarrow\text{a}:\text{b}=30:42$ and $\text{b}:\text{c}=42:77$

$\therefore\text{a}:\text{b}:\text{c}=30:42:77$

Hence, the correct alternative is option (b).