Inorganic phosphorous is a naturally occurring element in all plants and animals, with concentrations increasing progressively up the food chain (fruit < vegetables < cereals < nuts < corpse). Geochemical surveys take soil samples to determine phosphorous content (in ppm, parts per million). A high phosphorous content may or may not indicate an ancient burial site, food storage site, or even a garbage dump. Independent random samples from two regions gave the following phosphorous measurements (in ppm). Assume the distribution of phosphorous is mound-shaped and symmetric for these two regions. Region I: x1; n1 = 15
853 1,549 1,230 875 1,080 2,330 1,850 1,860
2,340 1,080 910 1,130 1,450 1,260 1,010
Region II: x2; n2 = 14
538 808 790 1,230 1,770 960 1,650 860
890 640 1,180 1,160 1,050 1,020
A button hyperlink to the SALT program that reads: Use SALT.
(a)
Use a calculator with mean and standard deviation keys to verify that x1, s1, x2, and s2. (Round your answers to four decimal places.)
x1 =
Correct: Your answer is correct.
ppm
s1 =

x2 =

s2 =

(b)
Let 1 be the population mean for x1 and let 2 be the population mean for x2. Find an 80% confidence interval for 1 − 2. (Round your answers to one decimal place.)
lower limit

upper limit