The instruction that came with this question said "do this in your head, do not use a calculator.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?
I reckon most here are going to get 5000 as an answer?
OK, then try doing what you have just done in your head on the calculator.
The answer is 4100.
What is happening here?
(PS I have no idea. Neither does the quite smart person who sent it to me).
How is this explained?