questioner wrote:

The correct answer should be 29 instead of 28: 15 - (-13) + 1, because 15 and -13 are both in the range inclusive.

15 and -13 are the maximum and minimum elements indeed, so to calculate the

**range **(the difference between the largest and the smallest numbers in a set) we do not need to add 1, it is just 15 – (-13) = 28 .

Here is an example of applying the formula to a non-integer values:

{-3.5, -2, 0.5, 4.3}

The range is 4.3 – (-3.5) = 7.8

The minimum element is not necessarily negative,

{2.5, 7, 15.4, 16.9}

The range is 16.9 – 2.5 = 14.4

As also the maximum element is not necessarily positive,

{-6, -3.1, -2.5}

The range is -2.5 – (-6) =3.5

However, remember, that range is always positive or zero (in case when all elements are the same).