I need to use exactly four (4) 100 ohm resistors in any combination of series and/or parallel circuits to give a total resistance of 40 ohms. I can't figure out how to combine them. I can only use 4 resistors, not more not less, and they must all be 100 ohm resistors.
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Put two resistors in series.
Then the other two in parallel.
Then both in parallel.
|--^^^^------^^^^-----|
|---------^^^^----------|
|---------^^^^----------|
Something like the above.
Then the other two in parallel.
Then both in parallel.
|--^^^^------^^^^-----|
|---------^^^^----------|
|---------^^^^----------|
Something like the above.