Question

HELP NEEDED !!!!

A class's exam scores are normally distributed. If the average score is 65 and the standard deviation is 6, what percentage of students scored below 71? Hint: Use the 68-95-99.7 rule.
A)34%
B)50%
C)68%
D)84%

Answer 1

The answer is Letter D - 84%

68% of the data is within +/- 1 SD from the mean = 59 to 7195% of the data is within +/- 2 SDs from the mean = 53 to 7799.7% of the data is within +/- 3 SDs from the mean = 47 to 83

The whole 68% (59 - 71) scored below 71. Since the data are evenly distributed, we'll get the 32% (100 - 68) outside the range of 68% and divide it by 2 and add the quotient to the original 68% so that we'll get the total data below 71.
100 - 68 = 32
32 / 2 = 16
16 + 68 = 84