Question

Cows in a herd graze in the sun. To protect themselves from the sun, they apply sunscreen. 2 mL of sunscreen protects an area of $50{\text{cm}}^2$ of skin. If Daisy the cow, has to protect an area of $4000{\text{cm}}^2$ of her skin with sunscreen then amount of sunscreen she would need is

Answer 1

We assume that Daisy would need $x$ mL of sunscreen for $4000{\text{cm}}^2$
Given that 2 mL of sunscreen is required for $50{\text{cm}}^2$ area of skin.
Since the amount of sunscreen Daisy needs to be apply must be proportional to the amount of sunscreen that needs to be applied to protect the her skin properly,
$2:50::x:4000$
$\Rightarrow \frac{2}{50}=\frac{x}{4000}$
By cross - multiplication, we get
$\Rightarrow 2\times 4000=x\times 50$
$\Rightarrow$ $x$ = 160
$\therefore$ Daisy would need $160$ mL of sunscreen to $4000{\text{cm}}^2$ area of her skin.