Question

If a : b = 3 : 1 and b : c = 5 : 1 then find the value of $\frac{a^2}{7bc}$.

• A. $\frac{25}{7}$
• B. $\frac{45}{7}$
• C. $\frac{15}{7}$
• D. $\frac{75}{7}$

Answer 1

The correct option is B $\frac{45}{7}$

Given a : b = 3: 1
$\Rightarrow a=3b$
and b : c = 5 : 1
$\Rightarrow b=5c$
$\Rightarrow a=15c$
Now, $\frac{a^2}{7bc}$ = $\frac{15c\times 15c}{7\times 5c\times c}$ = $\frac{45c^2}{7c^2}$ = $\frac{45}{7}$.

$\therefore$ $\frac{a^2}{7bc}$ = $\frac{45}{7}$