A wall 15 m long, 30 cm thick and 2 m high is built with bricks measuring 25 cm × 12.5 cm × 7.5 cm. Mortar fills one-tenth of the wall's volume. How many bricks are used?

Explanation

1. 01

   Wall volume = $1{,}500 \times 30 \times 200 = 90{,}00{,}000$ cm³.

2. 02

   Bricks fill nine-tenths of it: 81,00,000 cm³.

3. 03

   One brick = $25 \times 12.5 \times 7.5 = 2{,}343.75$ cm³.

4. 04

   Bricks = $81{,}00{,}000 \div 2{,}343.75 = 3{,}456$.