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Home > CCG > Chapter 8 > Lesson 8.2.1 > Problem 8-72


Sandip noticed that when he looked into a mirror that was lying on the ground  feet from him, he could see a clock on the wall. If Sandip’s eyes are inches off the ground, and if the mirror is feet from the wall, how high above the floor is the clock? Include a diagram in your solution.

Draw a diagram:

Two right triangles where the 90 degree angles are at the bottom left and right corners and one other vertex of each meet on the ground where the mirror is. The triangle on the left is 64 inches hight and 96 inches along the ground to the mirror. The triangle on the right is 120 inches from the mirror to the point directly below the clock.  The angles of both triangles at the mirror are the same.

Determine why the two triangles are similar. Remember triangles can be similar by AA, SAS, and SSS similarity theorems.

Set up a proportion. Are your units the same?

Solve the equation.