SOLUTION: A study found that 73% of elementary students buy lunch at school at least once a month. How large a sample would be necessary to estimate the true proportion within 3 percentage p
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Question 1161499: A study found that 73% of elementary students buy lunch at school at least once a month. How large a sample would be necessary to estimate the true proportion within 3 percentage points with 95% confidence? Answer by Boreal(15235) (Show Source):
You can put this solution on YOUR website! then half-interval or margin of error is 0.03=z*sqrt(p*(1-p)/n)
0.03=1.96*sqrt(0.73*0.27)/n)
square both sides
0.0009=3.8416*0.73*0.27/n
n=841.31 or 842
