Question

A water tank is 3/4 full.

56 litres of water are taken from the tank.

The tank is now 2/5 full.

Show clearly that the tank holds 160 litres when full.

Answer 1

x/.75=x-56/0.4

0.4x=.75x-42

-0.35x=-42

x=120

I set up a proportion in which x=the tank when it is 3/4 full. When the tank is 3/4 full, solving the proportion tells us the x=120 litres. 120/3=40, and 120+40 is 160, showing that a tank completely full would indeed hold 160 litres.

Hope this helps!