Could Someone Check My Statistics Review Sheet?

i was absent the day my professor went over the review sheet, and todays my test, i was hoping someone could help me by correcting me. i didn’t do the last 4 questions because i wasn’t sure what formula’s to use.
1) A company sells Ipods at a discount price to local Universities in California. In the past they found their monthly sales had a mean of $200 thousand dollars with a population standard deviation of $40 thousand dollars. For the next month, find the probability their monthly sales will be at least $220 thousand dollars?
Answser- z= 215000
2) A High School Valedictorian plans on going to Yale University next fall. She found out her grade point average must be within the top 2.17% of all high school GPA’s in the country. Based on last year’s population data, the mean GPA was 86 with a standard deviation equal to 5.941. Determine the minimum GPA she must receive in order to be accepted into Yale University.
answer= x=74
3) Suppose the average teacher’s salary in California is $52,174 and the distribution is normal with a population standard deviation equal to $7,500. If we sample 100 teacher’s salaries, what is the probability that the sample mean is less than $50,000?
z=0.0019
4) A sociologist develops a test to measure attitudes about public transportation and 37 randomly selected subjects are given the test. Their mean score is 76.2 and their population standard deviation is 21.4. Construct the 90% confidence interval for the mean score for all such subjects and interpret its meaning.
answer- (70.4,82)
5) A survey revealed the amount of pocket money held by each student from a random sample of 10 junior high school students. If the sample mean is $7.50 with a sample standard deviation of 0.75, find a 99% confidence interval for the population mean and interpret its meaning.
answer- (6.7,8.3)
6) A department store wants to estimate the mean time a customer waits on line. Given that
= 2.0 minutes, find the sample size of customers needed to ensure with 95% confidence that the sample mean will not differ by more than a margin of error of 0.2 minutes.
7) Suppose a health magazine reported 15% of all adults in the U.S. jog for exercise. A Gallup Poll recently asked 1500 adults whether if they jog for exercise or not. Find the probability the sample proportion is between 14% and 18%.
8) A survey of 50 first-time white water canoers showed that 23 did not want to repeat the experience. Find the 90% confidence interval of the true proportion of canoers who did not wish to canoe the rapids a second time.
9) A school administrator is concerned about the amount of credit-card debt that college students have. She wishes to conduct a poll to estimate the percentage of full time college students who have credit-card debt of $2,000 or more.
a) What size sample should be obtained if she wishes the estimate to be within 0.025 points with 98% confidence if a previous pilot study indicates that the percentage is 34%?
b) What size sample should be obtained if no previous estimate is known?

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