The first one is correct. The second one(proportion) should be 272 as the minimum sample size.
Hi guys!
THanks for all your help guys - esp Mr F!
I am stumped on these 2 questions! Any one have any idea on how to proceed?
Assuming the standard deviation for the cost of a bathroom remodel is known to be $545. How large a sample would need to be taken to estimate the mean cost of a bathroom remodel to within $136 with 99% confidence? I got 107 as my answer.
A researcher is interested in estimating the proportion of employees who are unhappy in their current. A prior study estimates this proportion at 0.13. How large a sample would need to be taken to estimate this proportion to within 4% with 95% accuracy? i got 71 as my answer
any help would be appreciated!
Cheers
Sunny
he z value for the 95% interval is 1.96.
The interval for a proportion is:
mean - sqrt(p(1-p)/N) to mean + sqrt(p(1-p)/N)
We want the sqrt(p(1-p)/N) to be 0.04:
0.04 = sqrt(p(1-p)/N)
p = 0.13
0.04 = sqrt(0.13*0.87/N)
0.04 = sqrt(0.1131/N)
Square:
0.1131/N = 0.0016
Multiply:
0.0016N = 0.1131
Divide:
N = 0.1131/0.0016
N = 70.6875
Round up:
N = 71