What is the mean of the numbers 80, 90, 100, 110?

• A. 85
• B. 90
• C. 95
• D. 100

Answer: (C)

The mean is found by adding all numbers and dividing by how many there are. Add them up: 80 + 90 + 100 + 110 = 380. There are four numbers, so 380 ÷ 4 = 95. So the mean is 95.

For four numbers that are evenly spaced, the mean also equals the average of the smallest and largest: (80 + 110) ÷ 2 = 95. This symmetry makes the mean (and typically the median) fall at 95.