Sulfur compounds cause "off-odors" in wine, so winemakers want
to know the odor threshold, the lowest concentration of a compound
that the human nose can detect. The odor threshold for dimethyl
sulfide (DMS) in trained wine tasters is about 25 micrograms per
liter of wine (μg/ l). The untrained noses of consumers may be less
sensitive, however.
You want to estimate the mean DMS odor threshold among all
students, and you would be satisfied to estimate the mean to within
±0.2 with 99 % confidence.
The standard deviation of the odor threshold for untrained noses
is known to be σ = 7 micrograms per liter of wine.
How large an SRS of untrained students do you need?