Solving for Resistance in a Circuit

[whoopie88]

Circuit Resistance Problem!

Homework Statement

The equivalent resistance between points A and B of the resistors shown in the figure below is 40 . Find the value of resistance R.

Homework Equations

All circuit formulas.

The Attempt at a Solution

40 - 12 = 28
28 = [(1/55) + (1/R)]^-1
R = -27

Help!

 

[SteamKing]

whoopie88:

Your equation for the unknown R is OK, but a mistake in your algebra has led you to find a negative solution. Retry your calculations carefully and see if you can't solve your equation properly.