A 25 m ladder leans against a vertical wall with its top 24 m above the ground. The top slips 4 m down the wall. By how much does the foot of the ladder move away from the wall?

Explanation

1. 01

   At first the foot is $\sqrt{25^2 - 24^2} = \sqrt{49} = 7$ m from the wall.

2. 02

   Now the top is at 20 m, so the foot is $\sqrt{25^2 - 20^2} = \sqrt{225} = 15$ m from the wall.

3. 03

   The foot moves $15 - 7 = 8$ m.