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The length of a rectangle is decreasing at 4 cm/minute and the width is increasing at 3 cm/minute. The rate of change of area when length is 10cm and width is 6cm, is:

Solution

✅ Correct Option: 3

With A=LWA = LW, dAdt=LdWdt+WdLdt\dfrac{dA}{dt} = L\dfrac{dW}{dt} + W\dfrac{dL}{dt}.

Substituting L=10L=10, W=6W=6, dLdt=−4\dfrac{dL}{dt} = -4 and dWdt=3\dfrac{dW}{dt} = 3:

dAdt=10(3)+6(−4)=30−24=6\dfrac{dA}{dt} = 10(3) + 6(-4) = 30 - 24 = 6 cm2^2/minute.

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