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

Answer 1

a = lw
da/dt = w dl/dt + l dw/dt
da/dt = 10*8 + 20*3 = 140 cm^2/s