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Posted by **bekah** on Sunday, January 2, 2011 at 11:32am.

The length of a rectangle is increasing at 3 ft/min and the width is decreasing at 2 ft/min. When the length is 50 ft and the width is 20 ft, at what rate is the rectangle decreasing?

- calc -
**Reiny**, Sunday, January 2, 2011 at 12:00pmLet the width of the rectangle be x ft

let the length of the rectangle be y ft

Area = xy

d(Area)/dt = x dy/dt + y dx/dt

given: dx/dt = -2 and dy/dt = 3

so when x = 20 and y = 50

d(Area)/dt = 20(3) + 50(-2)

= -40

At that moment, the area is**decreasing**at a rate of 40 ft^2/min

- calc -
**bekah**, Sunday, January 2, 2011 at 12:06pmthank you so much!!!!

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