A person is standing 40ft away from a street light that is 30ft tall. How tall is he if his shadow is 10ft long?

1 Answer
Gió
May 20, 2016

I got #6"ft"#

Explanation:

Considering the figure:
enter image source here
I would use trigonometry applied to the two triangles formed by the street light and the man writing:
Big one: #30/(40+10)=tan(alpha)#
Small one: #h/10=tan(alpha)#
substituting one into the other for #tan(alpha)# we get:
#30/50=h/10#
#h=30/50*10=6"ft"#
The two triangles are also similar so you can use the ratios of their sides and get the same result.

Related questions
See all questions in Solving Similar Triangles
Impact of this question
14181 views around the world
You can reuse this answer
Creative Commons License