A vessel full of water weighs 40 kg. If it is one-third filled, its weight becomes 20 kg. What is the weight…
A vessel full of water weighs 40 kg. If it is one-third filled, its weight becomes 20 kg. What is the weight of the empty vessel?
10 kg
15 kg
20 kg
25 kg
Solution
Let the empty vessel weigh $E$ and full water weigh $W$. Full: $E + W = 40$. One-third filled: $E + W/3 = 20$. Subtracting: $W - W/3 = 20$, so $2W/3 = 20$, giving $W = 30$ kg. Then $E = 40 - 30 = 10$ kg.