Simple addition

Do this in your head only. Do NOT use paper and pencil or a calculator. Add the following numbers as quickly as you can. Take 1000 and add 40 to it. Now add another 1000. Now add 30. Add another 1000. Now add 20. Now add another 1000. Now add 10. What is the total?

Now add the same numbers using a calculator.

Do your answers match?

I've done this five times and five times my answers have failed to match. (And I've been a member of MENSA since 1988! :eek: )