Find x, if 25 : x = x : 4

Side of a square is 4x. Its area is

A water tank contains 2/5 part water. When 250 litres of water is taken out, there remains 3/20 part of water in the tank. What is the volume of the tank?

A can do a piece of work in 5 days, B in 10 days. How long will they take to do it together?

If a side of a square is 10 metres, its area will be :

x + y = 48; x – y = 2. xy is: