# A tank measures 2m in length, 1.6m in width and 1m depth. Water is there upto 0.4m height. Bricks measuring 25cm?14cm?10cm are put into tank so that the water may come up to the top. Each brick absorbs water equal to 1/7th of its own volume. How many bricks will be needed?

water present = 2*1.6*0.4 = 1.28 m^3

volume of brick = 0.25*0.14*0.1 = 0.0035 m^3

water absorbed by each brick 1/7 * 0.035 = 0.0005 m^3

Let us say we need x bricks

Volume occupied by bricks x * 0.0035 m^3

Water remaining is 1.28 - x * 0.0005( initial water - water absorbed by bricks)

sum of both is the volume of the tank

0.0035x + ( 1.28 - 0.0005x ) = 3.2

0.003x = 3.2 - 1.28

0.003x = 1.92

x = 1.92/0.003 = 1920/3 = 640

so 640 bricks

reverse proof

Volume of bricks 640*0.0035

Initial volume of water 1.28

water absorbed by brick = 640*0.0035*1/7 = 640*0.0005

adding the 1st two and subtracting the 3rd we should get 3.2 m^3 the volume of the tank

640*0.0035 + 1.28 - 640*0.0005 = 3.2