<p>I remember how I became completely bemused when I first saw this (I've seen it before, it was in one of the practice tests)</p>

<p>Well, for starters, you should draw it. You'll notice that it is a 60-90-30 right triangle with 1 unknown side.The ladder is the base,the ground between the ladder and the wall is one of the sides and the wall's length - the other.The right angle, logically, is the space between the wall and the ground . You apply the pythagorean theorem to find the wall length .</p>

<p>7^2(the distance between the ladder and the building) +x^2(the wall on which the ladder is placed) = 25^2(ladder length)</p>

<p>You do the math and find out that the wall distance is 24.</p>

<p>Then you proceed to step 2 - the movement.</p>

<p>You know that the top of the ladder slides down 4 inches, which means that the bottom will also slide down , but you don't know how much, so you name it x. Consequently, if the ladder slides down the wall by 4 feet, the wall's length will be reduced by 4 feet as well.

24-4 = 20.</p>

<p>So, you've got yourself a triangle with 1 unknown side again. The ladder is 25 (as always) , since the ladder has slipped, the distance of the wall is 20 and you need to find the distance between the ladder's bottom and the wall. You set up a pythagorean theorem ,again.</p>

<p>20^2(the wall length + x^2 ( distance between the ladder's bottom and the wall) = 25^2 (the ladder length)</p>

<p>Great! You now know the distance has become 15. Before the ladder slipped it was 7. How longer it had become? 15-7 = 8.</p>

<p>Well, I hope you understood me. But personally I think an actual drawing on paper would be more apt to explain this one.</p>