In a chemistry lab have two distilled water tanks. Mary works in this lab, and make a riddle for Ann, your friend:
"The tank A have a half capacity of the tank B. These tanks are filled in half. They have this propriety: 'If the half of destilated water in the the tank A is put in the tank B, and after the 1/25 of distilled water in the tank B is put in tank A, the tank A finish with 3 liters of distilled water.' What is the capacity of the tank B?"