What is th meaning of this line

Question

the water proportion in the lean body mass(mass of the body - fat content) is a constant

Answer 1

the statement is not true ,

Answer 2

Say, I weigh 100 pounds, and about 60 pounds of that is water. Assuming I'm relatively lean (only 10% body fat), it would mean that my lean body mass is 90 pounds (mass of the body 100 lb - fat content 10 lb). So the water proportion in my lean body mass is 60 / 90 = 2/3

Now, say my brother is much fatter than me. He weighs 300 pounds, but is about 20% body fat. So his lean body mass is 240 pounds (mass of body 300 lb - fat content 60 lb). If 160 pounds of him is water, the water proportion in his lean body mass is also 2/3 (160 / 240), which is a constant.

Hope this helps.