If A : B = 3 : 7 and B : C = 2 : 5, find A : B : C.

Correct option is D

Given:
A : B = 3 : 7
B : C = 2 : 5,
Solution:​​
​$$\frac{A}{B} = \frac{3}{7} \quad \text{……(i)}\\\frac{B}{C} = \frac{2}{5} \quad \text{……(ii)}\\\text{Multiplying by 2 in (i) and by 7 in (ii) to make B the same in both ratios:}\\\frac{A}{B} = \frac{3 \times 2}{7 \times 2} = \frac{6}{14}\\\frac{B}{C} = \frac{2 \times 7}{5 \times 7} = \frac{14}{35}\\$$​​
Therefore,
A : B : C = 6 : 14 : 35
Alternate Method:

$$\begin{array}{c|c|c}A & B & C \\\hline3 & 7 & 7 \\2 & 2 & 5 \\\hline6 & 14 & 35\end{array}$$​