Question: How might stratification be used in each of the following sampling problems?
a. A survey of household expenditures in a city.
b. A survey to examine the lead concentration in the soil in a large plot of land.
c. A survey to estimate the number of people who use elevators in a large building with a single bank of elevators.
d. A survey of programs on a television station, taken to estimate the proportion of time taken up by advertising on Monday through Friday from 6 P.M. until 10 P.M. Assume that 52 weeks of recorded broadcasts are available for analysis.