Dylan Jones kept careful records of fuel efficiency of his new car. After the first nine times he filled up the tank, he found the mean was 27.5 miles per gallon (mpg) with a sample standard deviation of 1.4 mpg.
(a) Compute the 98 percent confidence interval for his mpg. (Round your answers to 3 decimal places.)
The confidence interval is between and .
(b) How many times should he fill his gas tank to obtain a margin of error below 0.15 mpg? (Round your answer to the nearest whole number.)
Number of time?