What is the equivalent resistance between points A and B in the figure when R = 20 Ω?
A)77 Ω
B)63 Ω
C)70 Ω
D)84 Ω
E)140 Ω

Question

What is the equivalent resistance between points A and B in the figure when R = 20 Ω? 
A)77 Ω 
B)63 Ω 
C)70 Ω 
D)84 Ω 
E)140 Ω

Quizplus · Accepted Answer

The circuit can be simplified by combining the 10Ω and 15Ω resistors in parallel to get a 6Ω equivalent resistance. Then, the two 6Ω resistors and the 20Ω resistor can be combined in series to get a total equivalent resistance of 38Ω. Finally, the 40Ω and 30Ω resistors in parallel can be combined to get an equivalent resistance of 12Ω. The 38Ω and 12Ω resistors can then be combined in series to get a total equivalent resistance of 50Ω. Thus, the answer is C) 70Ω.

What Is the Equivalent Resistance Between Points a and B