What is the formula for two resistors in a parallel circuit?

• A. Rt = R1 + R2
• B. Rt = (R1 x R2) / (R1 + R2)
• C. 1/Rt = 1/R1 + 1/R2
• D. Rt = R1 - R2

Answer: (B)

In a parallel circuit, the currents have separate paths, so the total resistance is reduced compared to either resistor. The relationship for two resistors is that the reciprocals add: 1/Rt = 1/R1 + 1/R2. From there, you can rearrange to Rt = (R1 × R2) / (R1 + R2). This direct form gives Rt outright, which is why it’s the clearest choice. It’s also the same idea as the reciprocal form, just expressed as Rt directly. The other options don’t describe parallel behavior: adding them would be for series, and subtracting them isn’t a standard parallel rule. For a quick check, if R1 and R2 are known, this formula yields a value smaller than either resistor, as expected in parallel.