**Question:**

How many bricks each of size 25 cm × 10 cm × 8 cm will be required to build a wall 5 m long, 3 m high and 16 cm thick, assuming that the volume of sand and cement used in the construction is negligible?

**Solution:**

Dimension of a brick $=25 \mathrm{~cm} \times 10 \mathrm{~cm} \times 8 \mathrm{~cm}$

Volume of a brick $=25 \mathrm{~cm} \times 10 \mathrm{~cm} \times 8 \mathrm{~cm}$

$=2000 \mathrm{~cm}^{3}$

Also, it is given that the length of the wall is $5 \mathrm{~m}$

$=5 \times 100 \mathrm{~cm}(\because 1 \mathrm{~m}=100 \mathrm{~cm})$

$=500 \mathrm{~cm}$

Height of the wall $=3 \mathrm{~m}$

$=3 \times 100 \mathrm{~cm} \quad(\because 1 \mathrm{~m}=100 \mathrm{~cm})$

$=300 \mathrm{~cm}$

It is $16 \mathrm{~cm}$ thick, i. e., breadth $=16 \mathrm{~cm}$

Volume of the wall $=$ length $\times$ breadth $\times$ height $=500 \times 300 \times 16=2400000 \mathrm{~cm}^{3}$

$\therefore$ The number of bricks needed to build the wall $=\frac{\text { volume of the wall }}{\text { volume of a brick }}=\frac{2400000 \mathrm{~cm}^{3}}{2000 \mathrm{~cm}^{3}}=1200$