Question 1156815
sigma known so use 1.96 for z
half-interval is1.99*19/sqrt(82)=4.11

the 95% CI is (224 mg, 232 mg)

The true value of the mean is unknown and unknowable, but we are 95% confident that it lies in the interval.

If we were to construct 100 such intervals like this one, the true mean would lie in 95 of them. We would not know which 95.