Average of Two Numbers Theorem

Suppose that you have three numbers a, b, and c with a sum of X.

Let W be the average of the first two numbers (a and b), and let P be the average of the last two numbers (b and c).

Then:

• W = (a + b) / 2
• P = (b + c) / 2
• The average of all three numbers is (W + P) / 2

For example, if a = 5, b = 10, and c = 15:

• W = (5 + 10) / 2 = 7.5
• P = (10 + 15) / 2 = 12.5
• The average of all three numbers is (7.5 + 12.5) / 2 = 10