Question

5. A monument casts a 78 ft. shadow at the same time that a vertical yardstick casts a 4.5 ft. shadow. How high is the monument?​

Answer 1

Hello,

Using Thalès 's theorem:

Let's h the height of the monument.

$\dfrac{1}{h} =\dfrac{4.5}{78} \\\\h=\dfrac{78}{4.5} =\dfrac{156}{9} \approx{17.3\ (ft)}$

If you don't know what is the Thalès's theorem,

imagine that the similar triangles.