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simulate this circuit – Schematic created using CircuitLab How R equivalent can be found (without using star delta connection)? the answer said 3/5R

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I don't know what you mean by "star delta" connection, but you should start by redrawing the schematic to be more clear:

enter image description here

This is the same circuit, but the resistors have been moved to make it more clear how they are connected. Obviously, R1 and R2 are in parallel, the resistance of R1||R2 is in series with R3, and the whole affair is in parallel with R4.

Solve by simplifying each parallel/series resistor pair to it's effective resistance.

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Delta or star are terms to describe how load, source or transformer is connected in 3 phase systems. Look here –  Kamil May 17 '14 at 8:06
@Kamil - I'm aware of the three-phase wiring schemes of the same name, but I don't see how they would apply at all to the OP's question, as it's a pure resistor simplification problem. –  Connor Wolf May 17 '14 at 9:17
@ConnorWolf A guess: The top 3 resistors are in a delta and transforming the delta to a star gives a topology which they my feel misses some point they are trying to make. –  Russell McMahon May 17 '14 at 14:28

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