CHAPTER 12

Inference for Means and Proportions

1. 
   

        In  a   study   to  see if  special exercises   help    babies  learn   to  walk    sooner, researchers randomly

   
   

   assigned 30 babies to experience the exercise regimen starting at the age of three months; 30 other
   babies were used as a control group and did not experience the exercises. The researchers recorded
   the age at which each baby first walked. A t -test for the difference in means yielded a P -value of
   0.56. What does this P -value mean in context?
   (A) There is a 56% chance that the exercises helped babies to walk sooner.
   (B) There is a 56% chance that there is no difference between babies who do the exercises and
   those who do not.
   (C) The exercises caused a 56% improvement in the time it takes for babies to walk.
   (D) If experiencing the exercises helps babies walk sooner, there is a 56% chance of seeing a
   difference as large as or larger than the one seen in this experiment.
   (E) If there is no difference between babies who experience the exercises and those who do not,
   there is a 56% chance of seeing a difference as large as or larger than the one seen in this
   experiment.

   
   


2. Seventy-five percent of crashes involving teen drivers were caused by errors on the part of the teen
   driver. A simple random sample of 80 crashes involving teen drivers is selected. The sampling
   distribution of the sample proportion has a mean of 0.75 and a standard deviation of
   (A) 0.0054.
   (B) 0.0484.
   (C) 0.0949.
   (D) 0.4330.
   (E) 3.8730.


3. A nutritionist was studying the effect of a particular diet on sleep loss in patients who had reported

difficulty sleeping. She conducted a test with the following hypotheses: H 0 : μ (^) N = μ (^) C where μ (^) N is the
mean number of hours of sleep for those on the new diet, and μ (^) C is the mean number of hours of sleep
for those in the control group.
H (^) A : μ (^) N > μ (^) C