Question

The grades on the last history exam had a mean of 80%. Assume the population of grades on history exams is known to be normally distributed with a standard deviation of 5. What percent of students earn a score between 70% and 80%?

Answer 1

80 - 70 = 10. The standard deviation is 5. Therefore the grade of 70% is 2 standard deviations below the mean. The empirical rule states that for all normal distributions approximately 95% of the data points lie within the range of plus and minus 2 standard deviations of the mean. In this case only half of the data points in this range are needed, so the required percentage is half of 95%.

Answer 2

thanks @kropot72

Answer 3

You're welcome :)