Parallel Resistance

The reciprocal of the total resistance of n resistors in parallel equals the sum of the reciprocals of each resistor.

frac{1}{R_{total}}=frac{1}{R_{1}}+frac{1}{R_{2}}+frac{1}{R_{n}}

frac{1}{R_{1}}=frac{1}{R_{total}}-frac{1}{R_{2}}-frac{1}{R_{n}}

frac{1}{R_{2}}=frac{1}{R_{total}}-frac{1}{R_{1}}-frac{1}{R_{n}}

etc.

More info: http://en.wikipedia.org/wiki/Series_and_parallel_circuits#Parallel_circuits