Plastic microparticles are contaminating the world's shorelines (see Exercise
6.108\()\), and much of this pollution appears to come from fibers from washing
polyester clothes. \({ }^{27}\) The worst offender appears to be fleece, and a
recent study found that the mean number of polyester fibers discharged into
wastewater from washing fleece was 290 fibers per liter of wastewater, with a
standard deviation of 87.6 and a sample size of 120 .
(a) Find and interpret a \(99 \%\) confidence interval for the mean number of
polyester microfibers per liter of wastewater when washing fleece.
(b) What is the margin of error?
(c) If we want a margin of error of only ±5 with \(99 \%\) confidence, what
sample size is needed?