Guillermo is 72 inches tall and casts a shadow of 24 inches. At the same time of day, his little sister casts a shadow of 20 inches. How tall is Guillermo's sister?
Let the little sister be
The sister is
The scenario presented can be shown as two similar triangles because the sun is shining at the same angle at the same time of day.
The sides of similar triangles are in the same ratio, so you can write a direct proportion.
As a check, we can see that the people are 3 times taller than the length of their shadows... This checks out in both cases.