The body of an adult is 70% water. What is the mass of water in the human body, which weighs 76kg.

First, find how much 1% of the weight of a person who weighs 76 kilograms is. To do this, divide 76 kilograms by 100. 76: 100 = 0.76 kilograms.
Next, we find the mass of water in a person. To do this, multiply 1%, which is 0.76 kilograms by 70. 0.76 * 70 = 53.2 kilograms.
Answer: 53.2 kilograms is the mass of water in a person who weighs 76 kg.