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Hi, I would be very grateful if anyone could shed some light on the below diagram as I'm trying to calculate the total resistance between A and B in this series parallel configuration.

10 and 20 are in parallel and 90, 70, and 80 are also in parallel but then I get confused with it as it then looks like two series circuits connected in parallel between A and B when you re-draw the diagram???


  • 2
    \$\begingroup\$ 90, 70, and 80 are not in parallel. 70 and 80 in parallel are in series with 60 which is all parallel with 90. \$\endgroup\$
    – Samuel
    Nov 1, 2013 at 19:29

2 Answers 2

  1. Re-draw your diagram


simulate this circuit – Schematic created using CircuitLab

If you can prove to yourself why these two circuits are equivalent, it should become apparent what is in parallel and what is in series.


Break the problem down so that eventually you end up with two parallel ( // ) resistance which will then give you the impedance between A &B.

LEFT of a --> b

X = 10//20 + 30 + 40


Y = (( 70//80 + 60 ) // 90 ) + 50

The: X // Y

This looks like homework though, so I shall leave it there ;)

  • \$\begingroup\$ Hi , Thanks to everyone for the great help as it can get somewhat frustrating at times but I have a much better understanding of it now. Cheers \$\endgroup\$
    – JFF
    Nov 1, 2013 at 21:26

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