This is really interesting. It's kind of a brain teaser.

Condition : You must do this in your head. Don't use paper to write out the problem.

Take 1000 and add 40 to it. Now add another 1000.
Now add 30. And another 1000.
Now add 20. Now add another 1000. Now add 10.

What is the total?



[Spoiler]Did you get 5000? Most people do, but the correct answer is actually 4100. If you don't believe me, try using a calculator or writing it on paper.[/Spoiler]

Thanks.