An element with a mass of 840 grams decays by 22.9% per minute. To the nearest minute, how long will it be until there are 70 grams of the element remaining?

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%)