Average from a base

mean

The trick, step by step

1. Choose a round base near the middle: 50.

   50

2. How far each number is from it: −3, +2, −1, +6.

   −3+2−1+6

3. Their total is 4, and 4 ÷ 4 = 1.

   1

4. So the mean is 50 + 1 = 51.

   51

given working answer taken away

Why it works

Each number is base + difference, so their mean is base + (the mean of the differences). The differences are small, so the sum is easy.