Question

An educational psychologist wishes to know the mean number of words a third grader can read per minute. She wants to ensure that the estimate has an error of at most 0.31 words per minute. A previous study found that the mean was 28.7 words per minute. Assuming that the variance is 6.76, what is the minimum number of third graders that must be included in a sample to construct the 85% confidence interval? Round your answer up to the next integer.

NASA is conducting an experiment to find out the fraction of people who black out at G forces greater than 6. In an earlier study, the population proportion was estimated to be 0.37.

How large a sample would be required in order to estimate the fraction of people who black out at 6 or more Gs at the 99% confidence level with an error of at most 0.04? Round your answer up to the next integer.

Answer 1

1)

	for85% CI crtiical Z          =	1.440
	standard deviation σ=	2.6
	margin of error E =	0.31
required sample size n=(zσ/E)2                  =		146

2)

here margin of error E =	0.04
for99% CI crtiical Z          =	2.576
estimated prop.=p=	0.3700
reqd. sample size n=	p*(1-p)*(z/E)2=	967

( please try 970 if critical z to 2 decimal places : 2.58 is to be used)