Question

We are trying to estimate the average score of students on the final for STAT 211. What sample size is necessary if we want to develop a 99% CI on the mean to within +/- 3 points? Past studies have indicated that the standard deviation for this score was somewhere between 5 and 8 points.

	a.	n = 39
	b.	n = 32
	c.	n = 48
	d.	n = 57
	e.	n = 55

Answer 1

We have given here,                  
                  
Population standard deviation =(5+8)/2=6.5..................Average value for 5 and 8  
Margin of error =E=3  
Level of significance =1-0.99=0.01  
Z critical value is (by using Z table)=   2.576  
Sample size formula is                   


=31.15          

b.   n = 32