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Review Problems for Test 2
Extra problems
1.
The average time it takes to take test 1 is 25 minutes with a standard deviation of 12 minutes.
The time it takes to take test 1 is known to be normally distributed.
a.
Describe this distribution.
X~N(25, 12)minutes
b.
What is the probability a randomly selected student will take less than 27 minutes to
take test 1?
i.
What is the random variable?
X= The average time it takes to take test 1
ii.
Describe this distribution.
X~N(25, 12)minutes
iii.
Can the probability be found?
Yes
iv.
If the probability can be found, what is it?
27
25
(
27)
(
)
12
(
27)
(
0.17)
(
27)
0.5675
P X
P Z
P X
P Z
PX
c.
If a random sample of 9 students is selected, what is the probability that the mean time
to take test 1 for these 9 students is less than 27 minutes?
i.
What is the random variable?
mean time to take test 1 for these 9 students
X
ii.
Describe this distribution.
12
(25,
)
9
XN
iii.
Can the probability be found?
Yes
iv.
If the probability can be found, what is it?
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This note was uploaded on 04/02/2011 for the course STAT 250 taught by Professor Sims during the Spring '08 term at George Mason.
 Spring '08
 sims
 Standard Deviation

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