Practice Assignment (to be discussed Wednesday, April 8)

1) Suppose that a commuter Alex wants to determine which of two possible routes gets him to work more quickly. Suppose that he drives route 1 for 10 days and route 2 for 10 days, recording the commuting times (in minutes) as follows:

Alex 1 19.3 20.5 23.0 25.8 28.0 28.8 30.6 32.1 33.5 38.4

Alex 2 23.7 24.5 27.7 30.0 31.9 32.5 32.6 35.5 38.7 42.9

(a) Construct side by side boxplots for the 2 routes.

(b) Find the p-value to decide if these sample commuting times provide evidence that the mean commuting times with these two routes differ.

2) Here are sorted commuting times on two routes for Barbara.

Barb 1 16.4 17.6 20.2 21.0 23.8 26.4 30.4 30.6 31.6 32.0

Barb 2 24.4 27.1 32.0 34.0 35.1 36.1 37.8 38.3 41.3 43.9

- Do steps (a) and (b) as above.

3) Here are sorted commuting times on two routes for Carl

Carl 1 23.7 24.3 25.5 26.8 28.0 28.4 29.3 30.1 30.6 33.3

Carl 2 27.7 28.5 29.1 30.2 32.1 32.4 34.0 34.6 35.3 36.1

- Do steps (a) and (b) as above.

4) Here are sorted commuting times on two routes for Donna.

Donna 1

10.1 13.5 20.9 21.7 23.7 22.8 23.0 23.5 24.0 24.8 24.9

25.0 25.8 26.0 26.1 26.5 26.6 26.7 27.1 28.0 28.4 28.5

28.9 29.0 29.3 29.8 30.1 30.0 30.2 33.2 32.4 33.3 33.4

33.8 33.8 34.0 35.3 36.6 39.5 39.9

Donna 2

20.4 22.4 24.2 24.4 24.4 25.0 25.4 25.6 26.2 27.2 27.7

28.6 28.9 28.9 29.4 29.5 30.4 30.4 31.0 31.2 32.4 32.5

33.8 33.9 34.0 34.9 35.4 35.5 35.5 36.1 36.4 36.6 37.2

37.3 37.5 38.0 39.7 41.5 44.4 46.2

- Do steps (a) and (b) as above.

Practice Assignment (to be discussed Friday, April 10)

1) In a 1990 study published in the Journal of Texture Studies, researchers studied the nature of sounds generated during eating. Peak loudiness (in decibels at a distance of 20 centimeters) was measured for both open-mouth and closed-mouth chewing of potato chips and of tortilla chips. Summary data for potato chips is below:

		sample size	samp mean	samp std dev
potato	open mouth	10	63	13
potato	closed	10	54	16

(a) Conduct the appropriate test of osignificance to assess whether the sample data provides evidence that "open mouth" chewing of potato chips tends to be louder than "closed mouth" chewing of potato chips. Report the hypohteses as well as the test statistic and p-value. Show the details of your calculations and conclusion.

2) In an experiment, individuals of different races and sexes visited car dealerships to request the best possible deal on a certain car. Below are the agreed upon prices in dollars.

	Dealership
	1	2	3	4	5	6	7	8	9
Black woman	4459	4320	4268	4585	4736	4262	4440	4398	4823
White man	4348	4385	4231	4516	4550	4203	4285	4408	4570

(a) Explain how you'd use randomization to carry out the experiment.

(b) Compute a 95% confidence interval for the true average difference between best price offered black females and white males. Do you conclude there is a difference?

(c) State the assumptions required by your procedures.

3) It is thought that the front cover and the nature of the first question on mail surveys influence the response rate. Researchers tested this theory by experimenting with different cover designs One cover was plain; the other used a picture of a skydiver. The researchers speculated return rate would be lower for plain cover.

(a) Does this data support the researchers' hypothesis?

(b) Estimate the difference between the rates.

(c) State the assumptions required by your procedures.