Clara recorded 50 numerical observations on a certain variable and then calculated the mean x¯ and the standard deviation s for the observations. To help decide whether a normal model is appropriate, she created the following chart. The figure presents a number line. The number line has four tick marks labeled from left to right as x bar minus 2 s, x bar minus s, x bar plus s, and x bar plus 2 s. The 4 tick marks create 5 intervals on the number line. From left to right the intervals are labeled a, b, c, d, and e. The intervals at the ends of the number line, a and e, appear to be the same length, the intervals labeled b and d appear to be the same length and the interval in the middle, labeled c, appears to be twice the length of interval b. In Clara’s chart, the letters a,b,c,d,and e represent the number of observations falling in each interval. Which of the following list of counts for a,b,c,d,and e, respectively, is the best indicator that the variable can be modeled with a normal approximation?
