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5.5 Part 1 Z-score Practice Due 2/13

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Question 1
1.

Nicole’s score on the Stats midterm was 82 points. The class average was 75 and the SD was 5 points.
What was her z-score?

Round your answer to three places if needed.

Question 2
2.

The speed of cars driving past DHS were measured, where the speed limit is 50 mph. The mean of 100 readings was 53.84 mph, with a standard deviation of 5.56 mph.

How many standard deviations from the mean would a car going the speed limit be?
Hint: this is the z-score.
Round to three places.

Question 3
3.

The speed of cars driving past DHS were measured, where the speed limit is 50 mph. The mean of 100 readings was 53.84 mph, with a standard deviation of 5.56 mph.

If a car’s z-score was +3.2, how fast was this car going?
Keep all places past the decimal, give units abbreviated (mph).

Question 4
4.

The speed of cars driving past DHS were measured, where the speed limit is 50 mph. The mean of 100 readings was 53.84 mph, with a standard deviation of 5.56 mph.

If a car was going 39 mph, how many standard deviations from the mean (z score) would this be?
Round to three places past the decimal

Question 5
5.

The speed of cars driving past DHS were measured, where the speed limit is 50 mph. The mean of 100 readings was 53.84 mph, with a standard deviation of 5.56 mph.

Which is more unusual, the car from #3 or the car from #4? (compare the z-scores)
Explain your answer.
Choose both correct answers below.

Question 6
6.

Question 7
7.

People with z-scores greater than 2.5 on an IQ test are considered as geniuses.
IQ tests have a score of a mean of 100 and SD of 16 points.

What is the cut off score to show someone is a genius? Hint: use the z-score.

Question 8
8.

Question 9
9.

Question 10
10.

A TV weatherman’s end-of-year analysis of the local weather showed that among all the years for which records had been kept, the past year’s average temperature
had a z-score of 2.8.
What does that mean? Hint: what does a z-score mean?

Question 11
11.
A highly selective university will only admit students who place at least 2 standard deviations above the mean on the ACT that follows the normal model: N(18, 6).
What is the mean? _______
What is the standard deviation? _______

What is the z-score for the minimum score that an applicant must obtain to be admitted
to the university? _______
What is the minimum score that an applicant must obtain to be admitted
to the university? _______
Question 12
12.

What if the mean score on our Stats Quiz yesterday was 75 points (hopefully not!) with a standard deviation of 5 points. If Marc’s z-score was 1.9, how many points did he score on the quiz?

Question 13
13.

Question 14
14.
A manufacturer of bolts has a quality control policy that requires it to destroy any bolts that are more than 2 standard deviations from the mean.
The quality control engineer knows that the bolts coming off the assembly line have a mean length of 8cm with a standard deviation of 0.05 cm.
For what length will a bolt be destroyed? Hint: you need to create an upper and a lower length that will cause the quality control engineer to throw away a bolt.

Shorter length for bolts to be thrown out: _______
Longer length for bolts to be thrown out: _______ include units!
Question 15
15.

because it is further away from the mean of zero.
The car going 71.632 mph is more unusual
The car going 39 mph is more unusual
Suppose your Statistics teacher reports test grades as z-scores and you got a score of 2.20 on an exam. Write a sentence explaining what that means.
Select both of the answers.
Your score is 2.2 points above the average score for the class.
Your score is 2.2 standard deviations above the average score for the class.
Your score is 2.2% above the average score for the class.
You did worse than a lot of the students in the class.
You did better than a lot of the students in the class.
Your score is 2.2 standard deviations below the average score for the class.
Your score is 2.2 points below the average score for the class.
Your score is 2.2% below the average score for the class.
IQ tests have a score of a mean of 100 and SD of 16 points.

If your IQ score was 122, what would your z-score be? Would this be considered unusual?
Select three correct answers.
This would not be unusual, it is less than 2 standard deviations from the mean.
This would be unusual, it is more than 2 standard deviations from the mean.
z-score = 1.375
z-score = -1.375
This would not be unusual, it is inside the central 95% of the IQ scores.
z-score = 122
This would be unusual, it is further out from the mean than the central 95% of the IQ scores.
IQ tests have a score of a mean of 100 and SD of 16 points.

If your IQ had a z-score of +2.5, what would your IQ score be? Would this be considered unusual?
Select three correct answers.
This would be unusual, it is more than 2 standard deviations from the mean.
This would be unusual, it is further out from the mean than the central 95% of the IQ scores.
IQ score = 140
IQ score = -100
IQ score = 125
This would not be unusual, it is inside the central 95% of the IQ scores.
This would not be unusual, it is less than 2 standard deviations from the mean.
The past year’s average temperature was 2.8% higher than the historical mean.
What if the mean score on our Stats Quiz yesterday was 75 points (hopefully not!) with a standard deviation of 5 points. If Cici scored a 78 on the Stats Quiz and a 86 on a Government Quiz that had a mean score of 83 and a standard deviation of 7 points, on which quiz did she score better on?
Calculate your work & explain. Hint: use z-scores to compare.
Choose all three correct answers.
and the highest z-score is the better quiz score compared to her class.
Cici scored better on the Government Quiz
because her z-score on the Stats Quiz was 0.429 and 0.6 on the Government Quiz
because her z-score on the Stats Quiz was 0.6 and 0.429 on the Government Quiz
Cici scored better on the Stats Quiz
and the z-score closer to the mean is the better quiz score compared to her class.
SAT vs. ACT- If you took the SAT and scored 550, and your friend took the ACT and scored 30. The SAT has a mean of 500 and a standard deviation of 100.
The ACT has a mean of 18 and a standard deviation of 6.

Which score is better?
Give the z scores.
Then explain.
Select 4 answers.
The SAT z-score =2.0
The SAT score is better
because the z-score is greater.
The ACT z-score = 2.0
The ACT z-score = 0.5
The ACT score is better
The SAT z-score = 0.5
because the z-score is closer to zero.