Question

Of 259 employees selected randomly from one company, 9.27% of them commute by carpooling. use this data to construct a 90% confidence interval for the true percentage of all employees of the company who carpool.

Answer 1

B. 14.4% < p < 22.9% 

std error = sqrt(.1867*(1=.1867)/225) = 0.025978 
t critical value for 224 degrees of freedom = 1.65168 

.1867-1.65168*0.025978 <= true proportion <= .1867+1.65168*0.025978 
.143793 <= true proportion <= .2299607