GATE 2015 EC – Question 17
In the network shown in the figure, all resistors are identical with $R = 300\ \Omega$. The resistance $R_{ab}$ (in $\Omega$) of the network is ________.
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Correct answer: 99.5 to 100.5
Explanation
The network is symmetric above and below the middle rail, so the middle nodes are at the same potential and can be joined. The upper half then reduces to $\frac{R}{6}$ in parallel groups, and so does the lower half. The total is $\frac{R}{6} + \frac{R}{6} = \frac{R}{3} = 100\ \Omega$.