# Q. 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?

(a) 10 kg

(b) 15 kg

(c) 20 kg

(d) 25 kg

Correct Answer: (a) 10 kg

#### Question from UPSC Prelims 2020 CSAT Paper

**Explanation :**

## Vessel full of water

When the vessel is full of water it weighs 40 kg. When it is one-third filled with water its weight becomes 20 kg. The difference in weight between these two states is 40 – 20 = 20 kg.

Since the only difference between these two states is the amount of water in the vessel, we can conclude that two-thirds of the water in the vessel weighs 20 kg.

So one-third of the water in the vessel weighs (20/2) = 10 kg.

Therefore, when the vessel is empty (i.e., when it has no water), its weight will be (20 – 10) = 10 kg.