Economics 120A
Name:
________key_________________
July 30, 2003
Student ID#: _________________________
ANSWER to Final Exam:
Econometrics
1.(10 points) The stamping machine on a production line periodically is taken off-line for
maintenance.
Assume that the amount of time the machine is off-line is uniformly
distributed between 15 and 30 minutes.
What is the probability that the machine is off-
line for more than 18 minutes? What is the probability that the machine is off-line
between 21 and 27 minutes?
(Answer)
(a) 18 to 30 minutes represent 80% of the distance between 15 and 30 minutes.
(b) The range 21 to 27 is 40% of the distance between 15 and 30 minutes.
2. (10 points) The length of time it takes to fill an order at a local sandwich shop is
normally distributed with a mean of 4.1 minutes and a standard deviation of 1.3 minutes.
If the sandwich shop employees make $6.00 an hour, what is the mean and standard
deviation for the labor costs per sandwich?
(answer)
E(X) = 4.1
sd(X) = 1.3
Labor cost per minute = $0.10
Y = 0.10X
E(Y) = (0.10)(4.1) = $0.41
sd(Y) = 0.1*sd(X) = 0.13.

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