when ryan runs the 400 m dash his finishing times are normally distributed with a mean of 75 seconds in your standard deviation of 0.5 seconds use in the empirical rule, determine the interval of times that represents the middle 68% of his finishing times in the 400 m race

Astudent must have an average on five test that is greater than it equal to 80% but less than 90% to receive a final grade of b. devon's greades on the first four test were 78% 62% 91% and 80% what range if grades on the fifth test would give him a b in the course? ( assuming the highest grade is 100%)