Question

Suppose a normally distributed set of data has a mean of 178 and a standard deviation of 20. Use the 68-95-99.7 Rule to determine the percent of scores in the data set expected to be below a score of 218. Give your answer as a percent and include as many decimal places as the 68-95-99.7 rule dictates. (For example, enter 99.7 instead of 0.997.)

Answer 1

97.7%

Explanation:

For a score below 218 :

P(x < 218)

Standard deviation = 20 ; mean = 178

Obtian the standardized score (Zscore) :

Zscore = (x - mean) / standard deviation

Z = (218 - 178) / 20 = 40 / 20 = 2

P(x < Z) = P(Z < 2) = 0.97725 (Z probability calculator)

0.97725 * 100 = 97.725 = 97.7%