Help with this one question! i will give brainlist

Select all the expressions that will include a remainder.

Determine if the equation defines y as a function of x: 2xy = 1. yes o no

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%)