statistics
posted by jessica knowes .
The Democrat and Chronicle reported that 25% of the flights arriving at the San Diego airport during the first five months of 2001 were late (Democrat and Chronicle, July 23, 2001). Assume the population proportion is p = .25.
1. Calculate () with a sample size of 1,200 flights (to 4 decimals).
2. What is the probability that the sample proportion will be within +/ .03 of the population proportion if a sample of size 1,200 is selected (to 4 decimals)?
3. What is the probability that the sample proportion will be within +/ .03 of the population proportion if a sample of size 600 is selected (to 4 decimals)?

bdjkgl

1) (sqrt(.25*(1.25))/1200) = .0125
2) .03/.0125 = 2.4 (zscore)
.03/.0125 = 2.4 (zscore)
Find value using standard normal distribution table:
2.4 = .9918
2.4 = .0082
.9918.0082 = .9836
3) (sqrt(.25*(1.25))/600) = .0177
.03/.0177 = 1.69 (zscore)
.03/.0177 = 1.69 (zscore)
Find value using standard normal distribution table:
1.69 = .9545
1.69  .0455
.9545  .0455 = .9090