When adding a zero to the numbers, the mean will get smaller.

Let us prove it by an example.

For example:

Let "2, 3, 5, 7, 9" be numbers that their mean is as follow.

m = (2+ 3 + 5+ 7+ 9) / total number

= ( 26 / 5) = 5.2

**The,n the mean = 5.2**

Now if we add zero, the numerator will remain the same while the denominator will increase by 1:

Then the denominator will be greater, then the mean is smaller:

Let us calculate:

m = ( 2+ 3 + 5+ 7+ 9 + 0) / 6

= ( 26)/6 = 4.333

**==> m = 4.33**