Three 10-ohm resistors in series have what total resistance?

• A. 3.3 ohms
• B. 10.0 ohms
• C. 40.6 ohms
• D. 30.0 ohms

Answer: (D)

When resistances are in series, you add them to get the total because the same current flows through each component and faces all of the opposition together. Add the values: 10 ohms plus 10 ohms plus 10 ohms equals 30 ohms. So the total resistance is 30 ohms. The other possible numbers come from different configurations or miscalculations: in parallel the total resistance is lower than any individual resistor, and with only one resistor in the circuit you’d just have that resistor’s value. But for three equal resistors in a straight series path, you simply add them.