Jane has found that the grade she earns on a test is determi

Jane has found that the grade she earns on a test is determined bu the number of hours spent studying for that test. This relationship is giving by the function y=0.55x + 76.8, where y is the grade earned on the test and x is the number of hours spent studying for the test. Solve the linear double inequality, 80<= 0.55x + 76.8 <= 89, using algebraic methods to determine how many hours Jane should study to earn a test grade between 80 and 89. Use interval notation when stating the solution.

The <= is less than equal to

Solution

80 <= 0.55x + 76.8 <= 89

subtract 76.8 from each side

80 - 76.8 <= 0.55x <= 89 - 76.8

3.2 <= 0.55x <= 12.2

divide by 0.55

3.2/0.55 <= x <= 12.2/0.55

5.82 <= x <= 22.18