If 12,000 72% C.I.'s were constructed, how many of those intervals would contain the true value of u? (thats supposed to be mu)
Ya gotta lurve elementary stats question with misleading wording.
About 72% of 12000 would be acceptable, but a single number is not.
(The probability of observing exactly 72% of 12000 CI containing the mean is ~0.8%)