## The age when smokers first start from previous studies is normally distributed with a mean of 13 years old with a population standard deviation of 1.3 years old

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##### Description

2)The age when smokers first start from previous studies is normally distributed with a mean of 13 years old with a population standard deviation of 1.3 years old. A survey of smokers of this generation was done to estimate if the mean age has changed. The sample of 33 smokers found that their mean starting age was 13.2 years old. Find the 90% confidence interval of the mean.

3)You are a researcher studying the lifespan of a certain species of bacteria.  A preliminary sample of 35 bacteria reveals a sample mean of ¯x=76x¯=76 hours with a standard deviation of s=4.4s=4.4  hours.  You would like to estimate the mean lifespan for this species of bacteria to within a margin of error of 0.8 hours at a 95% level of confidence.

What sample size should you gather to achieve a 0.8 hour margin of error? Round your answer up to the nearest whole number.

n =         bacteria

4) You are interested in estimating the the mean age of the citizens living in your community. In order to do this, you plan on constructing a confidence interval; however, you are not sure how many citizens should be included in the sample. If you want your sample estimate to be within 4 years of the actual mean with a confidence level of 90%, how many citizens should be included in your sample? Assume that the standard deviation of the ages of all the citizens in this community is 17 years.

Sample Size:

5) You measure 41 textbooks' weights, and find they have a mean weight of 35 ounces. Assume the population standard deviation is 12.2 ounces. Based on this, construct a 80% confidence interval for the true population mean textbook weight.

6) Given the interval estimate for the mean (9.4, 19.4), the point estimate for the mean is ?

and the margin of error is ?

7) You measure 42 textbooks' weights, and find they have a mean weight of 57 ounces. Assume the population standard deviation is 4.2 ounces. Based on this, construct a 99% confidence interval for the true population mean textbook weight. Round answers to at least 4 decimal places.

8) Given that x̄ = 39, n = 52, and σσ = 5, then we can be 95% confident that the true mean, μμ, lies between the values           and

9) If a school district takes a random sample of 64 Math SAT scores and finds that the average is 439, and knowing that the population standard deviation of Math SAT scores is intended to be 100. Find a 90 % confidence interval for the mean math SAT score for this district.

11) You measure 32 textbooks' weights, and find they have a mean weight of 76 ounces. Assume the population standard deviation is 14.9 ounces. Based on this, construct a 99% confidence interval for the true population mean textbook weight.

14) If n=19, ¯x(x-bar)=45, and s=2, find the margin of error at a 95% confidence level

15) In a survey, 7 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of \$37 and standard deviation of \$4. Find the margin of error at a 90% confidence level.