#### Question

A cistern, internally measuring 150 cm × 120 cm × 110 cm, has 129600 cm^{3} of water in it. Porous bricks are placed in the water until the cistern is full to the brim. Each brick absorbs one-seventeenth of its own volume of water. How many bricks can be put in without overflowing the water, each brick being 22.5 cm × 7.5 cm × 6.5 cm?

#### Solution

Volume of cistern = 150 × 120 × 110

= 1980000 cm^{3}

Volume to be filled in cistern = 1980000 − 129600

= 1850400 cm^{3}

Let *n* numbers of porous bricks were placed in the cistern.

Volume of *n* bricks = *n* × 22.5 × 7.5 × 6.5

= 1096.875*n*

As each brick absorbs one-seventeenth of its volume, therefore, volume absorbed by these bricks

= n/17(1096.875)

`1850400 + n/17 (1096.875) = (1096.875)n`

`1850400 = (16n)/17(1096.875)`

n = 1792.41

Therefore, 1792 bricks were placed in the cistern.