Question

If 10 pens cost ₹60 , what is the cost of 13 such pens?

Answer 1

Let us suppose the cost of 13 pens is ₹ x .
The number of pens and their cost vary in direct proportion.
$\therefore \frac{10}{60}=\frac{13}{x}$
$\therefore 10x=780$ (multiplying both sides by 60 x)
$\therefore x=78$
Cost of 13 pens is ₹78