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Stat 3011 section 13
Introduction to Statistics
Exam 2
November 9
th
, 2011
This exam is closed book. You are allowed a calculator and one 8 1/2 inch by 11 inch
piece of paper with notes. All other materials must be put away, including cell phones,
which must be off.
You have 50 minutes for the exam. Feel free to use the back of the page if you need
more space, but label any continued work clearly. Each answer is worth 10 points.
Problem 1
Below are descriptions of three different distributions. Identify whether the distribution is a data
distribution, population distribution, or sampling distribution. Also calculate any relevant
statistics±parameters for the distribution.
A) About one out of every ten children in the US has no health insurance.
Population distribution (5 points)
p=1/10 = 0.10 (or 10%) (5 points)
B) A random sample of 200 children in the US found that 16 had no health insurance.
Data distribution (5 points)
p
=
16
/
200
=
0.08 or 8
5 points
C) The proportion uninsured per sample for all random samples of size 200 of children in the US.
Sampling distribution (5 points)
µ
= p = 0.10 and se =
p
∗
1
−
p
n
=
.10
∗
.90
200
=0.021 (5 points)
Note: you didn't have to check to make sure the CLT conditions held to find the parameters because
they exist whether or not the sampling distribution is normal, but if you did, you'd see:
n*p = 200*.10 = 20
≥
15 and n*(1-p) = 200*.90 = 280
≥
15

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*Sign up*Problem 2
When driving, the time it takes people to respond to break lights in front of them is normally
distributed, with a mean of 1.25 seconds and a standard deviation of 0.46 seconds. Let's say that traffic
is moving on I-94 at a rate where there is about two seconds between each car. In other words, the time
between a car passing a point and the car behind it passing the same point is 2 seconds.
A) What is the probability that a driver is in an accident; i.e. what is the probability a randomly

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