How far would the top of the ladder move down?

Question

Suppose a ladder 20 feet long is place against a vertical wall 20 feet high. How far would the top of the ladder move down the wall by pulling out the bottom of the ladder 5 feet?

Answer 1

after the ladder is pulled out 5 ft, you have a right triangle with a hypotenuse of 20 and 1 side of 5.

Let h = the height

So using pythagorean Theorem 

20² = 5² + h²

h² = 400-25 = 375

h = √375 = 19.36 ft

top of ladder would move down 20-19.35 = 0.64 ft or 7.62 inches