### Assignment Instructions/ Description

The last option on part d is: Standard normal was used because "o"1 and "o"2 are unknown Image transcription textInorganic 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: x ; n, = 15

853

1,553

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: x,; n, - 14

542

312

790

1,230

1,770

960

1,650

860

890

640

1,180

1,160

1,050

1,020

LA USE SALT

(a) Use a calculator with mean and standard deviation keys to find x, and and s, (in ppm). (Round your answers to four decimal places.)

X 1

ppm

ppm

Use a calculator with mean and standard deviation keys to find x, and s2 (in ppm). (Round your answers to four decimal places.)

ppme

52

11

ppm

(b) Let , be the population mean for x, and let /, be the population mean for x, . Find an 80% confidence interval for , - /2. (Enter your answer in the form: lower limit to upper limit. Include the word "to." Round your numerical values to one decimal

1:place.)

ppm

4(c) Explain what the confidence interval means in the context of this problem. Does the interval consist of numbers that are all positive? all negative? of different signs? At the 80% level of confidence, is one region more interesting than the other from a

geochemical perspective?

Because the interval contains only positive numbers, we can say that Region I is more interesting than Region II.

Because the interval contains only negative numbers, we can say that Region II is more interesting than Region I.

4

| We can not make any conclusions using this confidence interval.

14) Because the interval contains both positive and negative numbers, we can not say that one region is more interesting than the other.

Hellojuli/() Which distribution (standard normal or Student's t) did you use? Why?

40O Student's t was used because o, and o, are known.

Standard normal was used because o, and o, are known.

1O Student's t was used because of and o, are unknown.

9:20 A

e

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