To estimate the mean score of those who took the medical college admission test on your campus, you will obtain the scores of an srs of students. from published information you know that the scores are approximately normal with standard deviation about 6.6 . you want your sample mean x¯ to estimate with an error of no more than 0.9 point in either direction. (a) what standard deviation must x¯ have so that 99.7% of all samples give an x¯ within 0.9 point of ? use the 68–95–99.7 rule. (enter your answer rounded to four decimal places.)