To find the volume of the tank, multiply the number of marbles by the volume of each marble and add the volume of water needed. The volume of the tank is 35 liters. To fill the tank with 20 liters of water, Andrei needs 450 marbles.
To find the volume of the tank, we need to multiply the number of marbles by the volume of each marble and add the volume of water needed to fill the tank.
In this case, Andrei used 50 marbles, each with a volume of 0.04 liters.
So the volume of the marbles is 50 x 0.04 = 2 liters.
Adding the 33 liters of water needed to fill the tank, the total volume of the tank is 2 + 33 = 35 liters.
To find out how many marbles Andrei needs to fill the tank with 20 liters of water, we need to subtract the volume of water already in the tank (2 liters) from the desired volume (20 liters) and divide by the volume of each marble (0.04 liters). So the number of marbles needed is (20 - 2) / 0.04 = 450 marbles.