How many items are in the event “exactly one tail” when a coin is flipped 3 times?
When a coin is flipped 3 times, there are 8 possible outcomes: HHH, HHT, HTH, THH, TTH, THT, HTT, TTT.
Out of these 8 outcomes, only 3 have exactly one tail: HHT, HTH, and THH.
Therefore, there are exactly 3 items in the event "exactly one tail" when a coin is flipped 3 times.