Question

The amount of water in a person's body varies directly with the person's weight. A person weighing $90kg$ contains $60$ litres of water. How many litres of water will a person weighing $50kg$ contain?

Answer 1

weight $\propto$ amount of water in body

weight $=K$ (amount of water)

$K=$ proportionality constant

$90=K\left(60\right)$

$\Rightarrow K=\frac{3}{2}$

$w=50kg$

$50=K$ (amount of water)

amount of water $=\frac{50}{K}=50\times \frac{2}{3}$

amount of water in $50kg=\frac{100}{3}kg$