Blair's average (arithmetic mean) on two physics tests is 7. What should Blair's score be on the next test to have an overall average of 8 for all the tests?
The correct answer is (D) 10. The arithmetic mean is defined as the sum of the terms divided by the number of terms.
7 = sum / 2
14 = sum
Adding the next test's score will change the average to an 8, and the total terms to 3.
8 = (14 + new score) / 3
24 = 14 + new score
10 = new score