\(\frac{sum of numbers}{number of numbers}\) =average, or \(\frac{sum of observations}{n}\)=arithmetic mean
We don't know what those numbers are so 'n'. The numbers are consecutive so we can minus one each time.
\(\frac{n+(n-1)+(n-2)+(n-3)+(n-4)}{5}\) = 2k-1
\(\frac{5n-10}{5}\)=2k-1
n-2=2k-1
n=2k+1

Sub in 2k+1 for the numbers above
2k+1, 2k, 2k-1, 2k-2, 2k-3

Difference is subtraction. Doesn't matter if they are positive or negative numbers, difference is still the same
(e.g. -5--2=-3=3, or if absolutes are familiar |-5|-|-2|=5-2=3
|2k+1|-|2k-3|
2k+3-2k+1 = 4

OR

5 Consecutive integers
5, 4, 3, 2, 1
5-1 = 4