A random sample of 45 doortodoor salespersons were asked how long on average they were able to talk to the potential customer. Their answers revealed a mean of 8.5 minutes with a variance of 9 minutes. Which Excel statement will calculate the margin of error?
a. 
=98.5 

b. 
=95 

c. 
=8.55 

d. 
=1.96*3/SQRT(45) 

e. 
=1.96*9/SQRT(45) 

f. 
None of the above. 
Solution :
Given that,
Point estimate = sample mean = = 8.5
variance = 9
Population standard deviation = = 3
Sample size = n = 45
At 95% confidence level the z is ,
= 1  95% = 1  0.95 = 0.05
/ 2 = 0.05 / 2 = 0.025
Z_{/2} = Z_{0.025} = 1.96
Margin of error = E = Z_{/2}* ( /n) = =1.96 * 3 / SQRT(45)
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