Question 1123366
Let the ladder be y feet above the ground and x feet from the wall
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use Pythagorean theorem 
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x^2 + y^2 = 25^2
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take first derivative of each vaiable with respect to time
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1)  2x * dx/dt + 2y * dy/dt = 0
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we are given dx/dt = 2 feet per second
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we want to find dy/dt when the ladder is 20 feet from the wall(x=20)
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when x=20
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20^2 + y^2 = 25^2
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400 + y^2 = 625
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y^2 = 225
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y = 15 feet (we ignore the negative root, -15)
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now use equation 1
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(2 * 20 * 2) + (2 * 15 * dy/dt) = 0
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80 + (30 * dy/dt) = 0
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dy/dt = -80/30 is approximately -2.67
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the velocity of the top of the ladder is -2.67 feet per second
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the velocity is negative because the top of the ladder is sliding down the wall
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