Question

Roushan bought $15$ lamps for $Rs.225,$ the cost of $9$ such lamps is

• A. $Rs.145$
• B. $Rs.135$
• C. $Rs.150$
• D. $Rs.110$

Answer 1

The correct option is B $Rs.135$

Let the cost of $9$ lamps be $Rs.x$

$\text{Lamps}$	$15$	$9$
$\text{Cost (in Rs.)}$	$225$	$x$

If he buys less number of lamps, the cost will also be less. Therefore, it is a direct variation.
We get:
$15:9=225:x$
$\Rightarrow \frac{15}{9}=\frac{225}{x}$
Applying cross multiplication, we get
$x=\frac{225\times 9}{15}=135$
Thus the cost of $9$ such lamps will be $Rs.135$