Section 8.3

#9. Given info:        n = 325,   p-hat = 295/325 = 0.908
We are to "test the claim that ... the probability of a baby being a girl is greater than 0.5," so one of our hypotheses must be "p>0.50." This can't be H0, since H0 must have an equal sign in it, so this must be H1. That tells us, then, that H0 must be "p = 0.50." Now see if you can do the test.

#11. Given info:        n = 11,000,   p-hat = 5720/11,000 = 0.52
We are to "test the claim that more than 50% of car crashes ...," so one of our hypotheses must be "p>0.50." This can't be H0, since H0 must have an equal sign in it, so this must be H1. That tells us, then, that H0 must be "p = 0.50." Now see if you can do the test.

#12. Given info:        n = 734,   p-hat = 360/734 = 0.490
We are to "test the claim that among Internet users, less than 50% use it ...," so one of our hypotheses must be "p<0.50." This can't be H0, since H0 must have an equal sign in it, so this must be H1. That tells us, then, that H0 must be "p = 0.50." Now see if you can do the test.

#14. Given info:        n = 1520,   p-hat = 58/1520 = 0.038
We are given that the rate was 0.058, and we are to "test the claim that the failure rate is now lower," so one of our hypotheses must be "p<0.058." This can't be H0, since H0 must have an equal sign in it, so this must be H1. That tells us, then, that H0 must be "p = 0.058." Now see if you can do the test.