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Statistics
Chapter 6 Review
Name ______________________________
Date _______________________
1. The percentage growth rate of stocks of companies that specialize in recreation equipment and appliances has a
mound shaped distribution with mean approximately 9.8 and standard deviation 3.8.
a) Estimate a range of values centered about the mean in which 68.2% of the data will fall.
b) Estimate a range of values centered about the mean in which 99.7% of the data will fall.
2. Lewis earned 85 on his biology midterm and 81 on his history midterm. In the biology class the mean score
was 79 with standard deviation 5. In the history class the mean score was 76 with standard deviation 3.
a) Convert each score to a standard z score.
b) On which test did he do better compared to the rest of the class? Explain.
3. Find the z value so that:
a) 8% of the area under the standard normal curve lies to the left of –z
b) 93% of the area under the standard normal curve lies between –z and z.
4. Leo has a pizza business. The times to prepare and deliver pizzas are approximately normally distributed with
mean   20 min and   10 min .
a) Suppose that Leo advertises “If it takes more than 30 minutes to get your pizza, you get it free”. What percent
of his take-out pizzas will he have to give away free?
b) How long a time should Leo allow if he wants to give away no more than 5% of the pizza?
5. Let x represent the life of a 60-watt bulb. The x distribution has a mean u  1000 hours with
Convert each of the following z intervals into x intervals.
a)
0  z  2.25
b)  1.5  z  1.4
  75 hours.
c) 1.35  z  3.25
6. On Professor Grindstone’s final exam the mean score was 280 and the standard deviation 15. He wants to
“curve” the exam so that the middle 50% of the students get C’s.
a) Find a z score for which the area under the standard normal curve from –z to z is 50%
b) Find the range of scores which will be assigned a grade of C.