Common difference between 31,26,21,16

I like to work backwards to see if the common difference is the same.

So I take 16 and work to the left.

So I say 16 - 21 which is - 5.

Then I do 21 - 26 which is - 5.

Finally, 26 - 31 which is - 5.

So what I am doing here is just taking the number that is on the right and subtracting it by the number that appears to the left of it.

Notice that I always get - 5 and that has to be because in order for this to have a common difference, the result must always be the same if you are working with the method I used above.

So, our common difference is - 5.