SOLUTION: I have knowledge about the calculating sample, but i am unable to solve this question for the last two hours. Please check this question. A bank believes that approximately 2/5

Question 1129685: I have knowledge about the calculating sample, but i am unable to solve this question for the last two hours. Please check this question.
A bank believes that approximately 2/5 of its checking-account customers have used at least one other service provided by the bank within the last six months.How large a sample will be needed to estimate the true proportion to within 5% at the 98% level of confidence?
Answer by rothauserc(4718) (Show Source): You can put this solution on YOUR website!
margin of error is 0.05
:
proportion = 2/5 = 0.40
:
alpha(a) = 1 - (98/100) = 0.02
:
critical probability(p*) = 1 - (a/2) = 0.99
:
the critical value(cv) associated with p* is determined from the table of z-scores
:
cv for a p* of 0.99 is 2.32
:
sample size = (2.32)^2 * (0.40) * (1-0.40) / (0.05)^2 = 516.7104
:
*****************************************************************************
With a proportion estimate of 2/5 at 98% confidence level, we need a sample
size of 517 to achieve a 5% margin of error for the survey of the
checking-account customers' proportion.
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:
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