Katie must take five exams in a math class. If her scores on the first four exams are 76, 74, 90, and 88, what score must Katie get on the fifth exam for her overall mean to be at least 70?
The mean is measured by taking the sum of the values and dividing by the count of values:
Katie has taken four exams already and is due to have her fifth, so we have
And now we solve for