Question

A cistern, internally measuring 150 cm × 120 cm × 110 cm, has 129600 cm3 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?

Answer 1

Volume of cuboid = lbh cu units
Hence volume of cistern = 150 × 120 × 110 cu cm
= 1980000 cu cm
Volume to be filled in the cistern = 1980000 − 129600
= 1850400 cu cm
Let the number of porous bricks placed in the cistern be ‘n’
Volume of each brick = 22.5 × 7.5 × 6.5 cu cm
Hence volume of ‘n’ bricks = n × 22.5 × 7.5 × 6.5 = 1096.875n
Given that each brick absorbs (1/17)th of its volume, t

herefore, volume absorbed by these bricks = (n × 22.5 × 7.5 × 6.5)/17
That is 1850400 + (n × 22.5 × 7.5 × 6.5)/17 = n × 22.5 × 7.5 × 6.5