In an issue of Newsweek (Vol. CXLV, No. 20, pp. 48–57), B. Kantrowitz listed “The 100 best high schools in America” according to a ranking devised by J. Mathews. Another characteristic measured from the high school is the percent free lunch, which is the percentage of student body that is eligible for free and reduced-price lunches, an indicator of socioeconomic status. A percentage of 40% or more generally signifies a high concentration of children in poverty. The top 100 schools, grouped according to their percent free lunch, is as follows.
Percent free lunch Number of top 100 ranked high schools
0–under 10 ............ 50
10–under 20 ............. 18
20–under 30 ............. 11
30–under 40 ............. 8
40 or over .............. 13
a. Use the table to design a procedure for obtaining a stratified sample of 25 high schools from the list of the top 100 ranked high schools.
b. If stratified random sampling with proportional allocation is used to select the sample of 25 high schools, how many would be selected from the stratum with a percent-free-lunch value of 30–under 40?