Assume that, on average, healthy young adults dream 90 minutes each night, as

inferred from a number of measures, including rapid eye movement (REM) sleep. An

investigator wishes to determine whether drinking coffee just before going to sleep

affects the amount of dream time. After drinking a standard amount of coffee, dream

time is monitored for each of 28 healthy young adults in a random sample. Results

show a sample mean,X, of 88 minutes and a sample standard deviation,s, of

9 minutes.

(a) Usetto test the null hypothesis at the .05 level of significance.

(b) If appropriate (because the null hypothesis has been rejected), construct a 95 percent

confidence interval and interpret this interval.