Sample size for proportion

Statistics
Tutor: None Selected Time limit: 1 Day

 a survey of people  reported that 55% of people said they had been in a tornado. How many people must be surveyed this year to estimate the percentage of people to be 95% confident that our estimate is within 5% of the true population percentage? 

Mar 14th, 2015

p =0.55

1-p=0.45

margin of error = 0.05

95% value =1.96

1.96 *sqrt(0.55*0.450/sqrt(n) =0.05

sqrt(n) = 1.96 *sqrt(0.55*0.45)/0.05 =1.96 *0.497494/0.05 =0.975088/0.05 =19.50

n =19.50^2 =380.3184 =381

sample size needed =381

Mar 14th, 2015

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