The length of a rectangle is increasing at a rate of 8 cm/s and its width is increasing at a rate of 3 cm/s. when the length is 20 cm and the width is 10cm, how fast is the area of the rectangle increasing

Let l = length of the rectangle,
b = breadth of the rectangle,
a = area of the rectangle,
t = time,

So, = 8 cm/s &
= 3 cm/s

Area of the rectangle, a = l × w

Differentiate the equation with respect to t,

= l × +  w × 

= 20 × 3 +  10 × 8

= 60 +  80

= 140 /s

Therefore, the correct answer is 140 /s.

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