5 Mary is hiking a trail in the hills. After 30 minutes, she is at an elevation of 550 feet. After 60 minutes, she is at an elevation of 1000 feet. What is the average rate of change (feet per minute) for elevation?

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%)