Word problem with inequalities

Question

Your math test scores are 68,78,90, and 91. What is the lowest score you can earn on the next test and still achieve an average of at least 85?

Answer 1

Average is (sum of values) / (count of values).

"At least" means "≥"

 

So,

      (68 + 78 + 90 + 91 + x)/5 ≥ 85

 

       (327 + x) / 5 ≥ 85

        327 + x  ≥  425          [multiply both sides by +5 retains sense of inequality]

         x ≥ 98

The lowest score that you can earn on the next test and still achieve an average of at least 85 is 98.