Combination of Resistors
In the given circuit all resistances are of value each. The equivalent resistance between and is:

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Answer: (a)
- Find the plain wires: the middle horizontal wire, the central vertical wire and the lower-left horizontal wire join the left-middle, centre, bottom-left and bottom-centre dots into one node.
- So the resistor from A and the resistor from B both end on this same node; the rest of the network is attached only to that one node, so it carries no current.
- Only the two series resistors at A and at B remain: .
- So the answer is (a) .