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HW 1 SOLUTIONS
1. For each of the following settings:
(i) identify the variable(s) in the study,
(ii) for each variable tell the type of variable (e.g., categorical and ordinal, discrete, etc.),
(iii) identify the observational unit, and
(iv) determine the sample size.
a. A botanist grew 15 pepper plants and measured the stem length in centimeters after 21 days of growth.
Correct:
(i) stem length
(ii) quantitative and continuous
(iii) pepper plant
(iv) 15
b. As a part of a classic experiment on mutations, ten aliquots (a part of the culture) of identical size were
taken from the same culture of the bacterium
E. coli
. For each aliquot, the number of bacteria resistant to a
certain virus was determined.
Correct:
(i) number of resistant bacteria
(ii) quantitative and discrete
(iii) aliquot
(iv) 10
c. A geneticist observed 234 progeny from selfpollinating pinkflowered snapdragon plants for their color.
Correct:
(i) color
(ii) qualitative and nominal
(iii) snapdragon progeny
(iv) 234
2. Consider the following fictitious data set.
Note
, there are no units for this data set.
23, 29, 24, 21, 23
a. Compute the mean.
Correct:
(23 + 29 + 24 + 21 + 23) / 5 = 24
b. Compute the sample standard deviation.
Correct:
We compute the mean to be 24.
s
2
= [(2324)
2
+ 2924
2
+ (2424)
2
+ (2124)
2
+ 2324)
2
]/4 = [1 + 25 + 0 + 9 + 1]/4 = 9
s =
√
s
2
= 3
c. It's easy to see that the median for this fictitious data set is 23 and you computed the mean in part (a).
Consider replacing the value 24 in this data set with the value 29. Using this new data set, calculate the mean
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 Fall '09
 Hendrix

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