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 H_{0}, since H_{0} must have an equal sign in it, so this must be H_{1}. That tells us, then, that H_{0} 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 H_{0}, since H_{0} must have an equal sign in it, so this must be H_{1}. That tells us, then, that H_{0} 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 H_{0}, since H_{0} must have an equal sign in it, so this must be H_{1}. That tells us, then, that H_{0} 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 H_{0}, since H_{0} must have an equal sign in it, so this must be H_{1}. That tells us, then, that H_{0} must be "p = 0.058." Now see if you can do the test.