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## Homework Statement

http://img514.imageshack.us/img514/1223/questionju1.jpg [Broken]

## Homework Equations

Parallell: [tex]\frac{1}{R_{eq}} = \frac{1}{R_{1}} + \frac{1}{R_{2}}[/tex]

Series: [tex]R_{eq} = R_{1} + R_{2}[/tex]

## The Attempt at a Solution

Part 1 - When the switch is not closed:

[tex]R_{eq_2} = R + ((90+10)^{-1} + (90+10)^{-1})^{-1}[/tex]

[tex]R_{eq_1} = R + 50[/tex]

Part 2 - When the switch is closed:

[tex]R_{eq_2} = R + (90^{-1} + 10^{-1})^{-1} + (90^{-1} + 10^{-1})^{-1}[/tex]

[tex]R_{eq_2} = R + 18[/tex]

Since [tex]R_{eq_1} = 2R_{eq_2}[/tex], then

[tex]R + 50 = 2(R + 18)[/tex]

[tex]R + 50 = 2R + 36[/tex]

[tex]R = 14[/tex]

The answer in the back, though, is 24. What have I done wrong?

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