Question

The weight of $72$ books is $9\mathrm{kg}$. What is the weight of $40$ such books?

Answer 1

Weight of $72$ books$=9\mathrm{kg}$

Weight of one book$=\frac{9}{72}\mathrm{kg}$

Weight of $40$ books$=\frac{9}{72}\times 40=5\mathrm{kg}$

Hence, $40$ books will weigh $5\mathrm{kg}$.