Question

At a certain time of the day, a tree 15 m tall casts a shadow of 12 m, while a second tree casts a shadow of 20 m. How tall is the second tree?

Answer 1

We can write a proportion: 15 m is to 12 m as some other height $h$ is to 20 m

So we get
$\frac{15}{12}=\frac{h}{20}$
$\rightarrow 15*20=12h$
$\rightarrow 12h=300$
$\rightarrow h=25$

So the second tree is 25 m tall.