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February 24th, 2013, 06:11 PM  #1 
Newbie Joined: Feb 2013 Posts: 2 Thanks: 0  statistics. Please help!!
Can someone please help me with these statistics questions? This subject is a little confusing so any help would be appreciated. 1. In a random sample of 500 college students at WVU, 72% indicated they preferred to study while listening to music or some kind of background noise while others indicated they liked to study in a quiet setting. What is the 99% confidence interval for music/background noise studying? a. 72 ± 3.44 b. 72 ± 14.14 c. 72 ± .72 d. 72 ± 9.83 e. None of the above 2. Suppose that you're thinking about buying a used Rcar at Honest Abe's. In order to make an informed decision you look up the records in an auto magazine and find that 30% of these cars have a faulty transmission. To get more information you hire a mechanic who is excellent: Of all the faulty cars he has examined in the past he correctly judged that 90% were "faulty" and only erroneously judged 10% as "OK." He 's almost as good at judging good cars: Of all the good cars he's correctly judged that 80% were "good" and only erroneously judged 20% as "faulty." What is the probability that the Rcar you're thinking of buying has a faulty transmission if the mechanic judges it to be "OK"? a. .05 b. .10 c. .17 d. .55 e. .27 3. Walter's Trucking determined that on an annual basis, the distance traveled per truck is normally distributed with a mean of 50 thousand miles and a standard deviation of 12 thousand miles. What is the probability that a randomly selected truck travels between 34 and 38 thousand miles in a year? a. .0669 b. .1124 c. .4357 d. .6151 e. .1345 4. Walter's Trucking determined that on an annual basis, the distance traveled per truck is normally distributed with a mean of 50 thousand miles and a standard deviation of 12 thousand miles. What percentage of trucks can be expected to travel either below 30 or above 60 thousand miles in a year? a. .8814 b. .2518 c. .3618 d. .0453 e. .5557 5. Suppose that you're thinking about buying a used Rcar at Honest Abe's. In order to make an informed decision you look up the records in an auto magazine and find that 30% of these cars have a faulty transmission. To get more information you hire a mechanic who is excellent: Of all the faulty cars he has examined in the past he correctly judged that 90% were "faulty" and only erroneously judged 10% as "OK." He 's almost as good at judging good cars: Of all the good cars he's correctly judged that 80% were "good" and only erroneously judged 20% as "faulty." What is the probability that the Rcar you're thinking of buying has a faulty transmission before you hire the mechanic? a. .27 b. .24 c. .30 d. .20 e. .41 6. Walter's Trucking determined that on an annual basis, the distance traveled per truck is normally distributed with a mean of 50 thousand miles and a standard deviation of 12 thousand miles. How many miles will be traveled by at least 80% of the trucks? a. 7500 b. 55600 c. 41500 d. 39920 e. 12000 7. Walter's Trucking determined that on an annual basis, the distance traveled per truck is normally distributed with a mean of 50 thousand miles and a standard deviation of 12 thousand miles. What proportion of trucks can be expected to travel between 34 and 50 thousand miles in a year? a. .4082 b. .5154 c. .6670 d. .4750 e. .2659 8. Suppose that you're thinking about buying a used Rcar at Honest Abe's. In order to make an informed decision you look up the records in an auto magazine and find that 30% of these cars have a faulty transmission. To get more information you hire a mechanic who is excellent: Of all the faulty cars he has examined in the past he correctly judged that 90% were "faulty" and only erroneously judged 10% as "OK." He's almost as good at judging good cars: Of all the good cars he's correctly judged that 80% were "good" and only erroneously judged 20% as "faulty." What is the probability that the Rcar you're thinking of buying has a faulty transmission if the mechanic judges it to be "faulty"? a. .72 b. .80 c. .16 d. .66 e. .30 
February 24th, 2013, 06:53 PM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs  Re: statistics. Please help!!
Posting 8 questions (we recommend only 1 or 2 questions per topic) with no work at all shown will most likely deter most of our contributors from helping.

February 24th, 2013, 06:59 PM  #3 
Newbie Joined: Feb 2013 Posts: 2 Thanks: 0  Re: statistics. Please help!!
I understand that 8 questions is quite a lot, this is why I am asking for any kind of contribution, not necessarily everything. Like I said, this topic is a bit confusing so any kind of help will work.

February 25th, 2013, 04:59 AM  #4 
Math Team Joined: Apr 2010 Posts: 2,780 Thanks: 361  Re: statistics. Please help!!
What is confusing about it? 3. Have you ever used zscores? 8. How many cars really are faulty? What cases does the mechanic judge it faulty? 

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