CPM Homework Help : CCG Problem 5-92

Triangle, A D E, horizontal base, A D, with horizontal segment, B C, drawn inside. In the diagram at right, $ΔABC$ and $ΔADE$ are similar. If $AB=5$ , $BD=4$ , and $BC=7$ , then what is $DE$ ?

Hint:

Separate the triangles into two similar triangles.

More Help:

What is the length of $AD$ ? Once you know this, since the triangles are similar, the ratios of corresponding sides are equal.
Remember to set up proportions.

Answer:

$DE=12.6$ units