Chapter 4.1, Problem 4E

For the following exercises, sketch the situation if necessary and used related rates to solve for the quantities.

4. [T] If two electrical resistors are connected in parallel, the total resistance (measured in ohms, denoted by the Greek capital letter omega, Q) is given by the equation $\frac{1}{R}=\frac{1}{R_1}+\frac{1}{R_2}$ . If $R_1$ is increasing at a rate of $0.5\Omega /\min$ and $R_2$ decreases at a rate of $1.1\Omega /\min$ , at what rate does the total resistance change when $R_1=20\Omega$ and $R_2=50\Omega /\min$ ?