Question

A statue of George Washington is also in Druid Hill Park. If a girl stands 15 m away from the statue, and places a mirror 12 m from the statue (3 m from her feet), she can see the top of the statue in the mirror. The girl's height is 5.5 ft. How tall is the statue?

Answer 1

The statue is 22ft tall.

Explanation:

Here we will have two similar triangle rectangles.

One is made between the girl's feet, the mirror, and the girl's eyes.

So in this case the catheti are:

the distance between the girl and the mirror (3 m) and the height of the girl (5.5 ft)

The other triangle rectangle has the vertices:

The mirror, the base of the statue, and the top of the statue.

Such that the catheti of this triangle are the distance between the base of the statue and the mirror (12m) and the height of the statue (we want to know this, let's call this X for the moment).

Because the triangles are similar, this means that there is a proportionality constant between each correspondent side, let's call this k.

Then the distance between the girl and the mirror must be k times the distance between the base of the statue and the mirror:

3m = k*12m

And the height of the girl must be k times the height of the statue.

5.5ft = k*X

You can see that we have different units, this does not matter because k is a dimensionless constant.

With the first equation we can find the value of k

3m = k*12m

3m/12m = k

(3/12) = 1/4 = k

Now we can replace this in the other equation to get:

5.5ft = (1/4)*X

Solving this for X we get:

(5.5ft)*4 = X

22ft = X

The height of the statue is 22ft.