The amount of money spent on textbooks per year for students is approximately normal. a. To estimate the population mean, 19 students are randomly selected the sample mean was $390 and the standard deviation was $120. Find a 95% confidence for the population meam.
b. If the confidence level in part a changed from 95% 1to1999%, would the margin of error for the confidence interval (mark one answer): decrease stay the same increase not enough information to answer
c. If the sample size in part a changed from 19 10 22. would the margin of errot for the confidence interval (mark one answer): decrease in stay the same increase in not enough information to answer
d. To estimate the proportion of students who purchase their textbookslused, 500 students were sampled. 210 of these students purchased used textbooks. Find a 99% confidence interval for the proportion of students who purchase used text books.

a

a

b

  The  margin of error will increase

c

The  margin of error will decreases

d

The 99% confidence interval is  

Step-by-step explanation:

From the question we are  told that

   The sample size  

    The sample mean is  

    The  standard deviation is  

Given that the confidence level is  95% then the level of significance is mathematically represented as

Next we obtain the critical value of from the normal distribution table

    So  

The  margin of error is mathematically represented as

=>    

=>  

The 95% confidence interval is  

=>  

=>  

When the confidence level increases the also increases which increases the margin of error hence the confidence level becomes wider

Generally the sample size mathematically varies with margin of error as follows

So if the sample size increases the margin of error decrease

The  sample proportion is mathematically represented as

Given that the confidence level is 0.99 the level of significance is  

The critical value of from the normal distribution table is  

  Generally the margin of error is mathematically represented as

=>  

=>    

The 99% confidence interval  is

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step-by-step explanation:

a=24; b=12

step-by-step explanation:

a/b=2: 1

a=2b

36/(1+2)=12

b=12

a=24