A student earned 81, 71, 78, 69 - hat do they need to score on the next test to have an average of 80.
To find an average or mean, you need to add up all of the values and divide it by the number of values. However, you are missing the value you're trying to find.
81 + 71 + 78 + 69 + x / 5 = 80
Solve for x. Multiply both sides by 5 to remove it from being a fraction and simplify.
299 + x = 400
Subtract 299 from both sides and x = 101. They need to score a 101 to get an average of 80.
To check our work, plug in 101.
81 + 71 + 78 + 69 + 101 / 5 = 80
80 = 80