STAT 200 QUIZ 1 Solutions
Section 6380
Fall 2013
•
The quiz covers Chapters 1, 2 and 3.
(For Questions 1 to 6) The checkout times (in minutes) for 12 randomly selected
customers at a large supermarket during the store’s busiest time are as follows:
4.6
8.5
6.1
7.8
10.7
9.3
12.4
5.8
9.7
8.8
6.7
13.2
1.
(2 points)
(Show work)
What is the mean checkout times based on the 12
checkout times.
The mean checkout time based on the raw data
= (4.6 + 8.5 + 6.1 + 7.8 + 10.7+ 9.3 + 12.4 + 5.8 + 9.7 + 8.8 + 6.7 + 13.2) / 12 = 103.6 / 12
= 8.63
2. (6 points)
(Show work)
Give a 5-number summary of the checkout time, and
construct the corresponding boxplot.
Arrange the checkout times from low to high:
Method 1 : Use the approach from the book
Location
1
2
3
4
5
6
7
8
9
10
11
12
Data
4.6
5.8
6.1
6.7
7.8
8.5
8.8
9.3
9.7
10.7
12.4
13.2
Minimum: 4.6
Q
1
: Find the location L of the 25
th
percentile in the sorted list:
25
1
12
.12
3
100
100
4
k
L
n
=
⋅
=
⋅
=
Because L = 3 is a whole number, the 25
th
percentile (first quartile) is located between 3
rd
and 4
th
checkout time in the sorted list. The 3
rd
and 4
th
checkout times are found to be 6.1 and 6.7, so the
first quartile Q
1
is (6.1 + 6.7) / 2 = 6.4 minutes

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