I'm an ASE certified Technician specializing in Brakes and Four-wheel Alignments. I'm going to go for my cert. in Electrical systems this fall. As I began my self-study in electrical systems, I realized.....I forgot my Algebra. I'm currently studying Ohm's Law. Within Ohm's Law, I'm studying Resistance in a parallel circuit. The formula I'm given is: R0=1/(1/R1) + (1/R2) = (R1 x R2)/(R1 + R2) .....where R0 (read R-sub0) is a combination of resistances R-sub1 and R-sub2. I thought the sum of the resistances in any circuit was R0=R1+R2. Why is 1 divided by (1/R1) + (1/R2) and in the "denominator portion" of the formula, why is 1 divided by R1 (same question for 1 divided by R2) and then added to 1/R2? Also, how do you get from R0=1/(1/R1) + (1/R2) to (R1 x R2)/(R1 + R2)?