If you wire two 12-millihenry chokes in series, what is the inductance of the combination?

When inductors (often called chokes) are wired in series, their inductance values simply add together. This is because the magnetic field from each inductor contributes to the total opposition to the change in current. The formula for inductors in series is exactly the same as for resistors in series: L_total = L1 + L2 + L3, and so on. Therefore, by placing two 12-millihenry chokes in series, you add 12 and 12 to get a total inductance of 24 millihenries. The distractor of 6 millihenries would only be correct if the chokes were wired in parallel.