Six different national brands of chocolate chip cookies were randomly selected at the supermarket. The grams of fat per serving are as follows: 8; 8; 11; 7; 9; 9. Assume the underlying distribution is approximately normal. NOTE: If you are using a Student's t-distribution, you may assume that the underlying population is normally distributed. (In general, you must first prove that assumption, though.) O Part (a) Construct a 90% confidence interval for the population mean grams of fat per serving of chocolate chip cookies sold in supermarkets. ) State the confidence interval. (Round your answers to two decimal places.) 7.23 10.11 (ii) Sketch the graph. 0.025 C.L. = 0.95 0.025 7.23 10.11 (i) Calculate the error bound. (Round your answer to two decimal places.) 1.44 O Part (b) If you wanted a smaller error bound while keeping the same level of confidence, what should have been changed in the study before it was done? O decrease the sample size O increase the sample size O determine the population standard deviation O nothing can be changed to guarantee smaller error bound