Question

Note: I am using the TI-84 Plus Silver Edition with this problem, but I can't seem to get the same answer as the book. May someone please let me know what I am doing wrong?

A survey of all medium- and large-sized corporations showed that 64% of them offer retirement plans to their employees. Let pˆ be the proportion in a random sample of 50 such corporations that offer retirement plans to their employees. Find the probability that the value of pˆ will be greater than 0.71

Book's Answer = 0.1515

My work:

p = .64

q = 1 - p = 1 - .64 = .36

n = 50

mean = p = .64

standard deviation of p-hat = sqrt(p*q/n) = sqrt(.64*.36/50) = .0679

Calculator's Input:

2nd -> DISTR -> normalcdf(Lower Bound, Upperbound, Mean, Standard Deviation) = normalcdf(0.71, 1E99, 0.64, sqrt(.64*.36/50)) = .1512873486

Therefore my answer is, P(p-hat > .71) = 0.1513

In the end, I am 0.0002 off after rounding.

Answer 1

nothing is wrong in your work. I have checked it by 2 ways but i am also getting same answer as yours. 0.0002 error is negligible error so your answer is also correct