You have number 1000. Now add 40. Now add again 1000. Now add 30. And again add 1000. Now add 20. Add again 1000. And finally, add 10.
.... Did you get 5000 ? Actually, the real result is 4100. Maybe some of you did get the real result! :D
Next... here's a little picture... sorry, it isn't perfect. OK, the task is:
This is a prison. You are person number 1. EN- ENTRANCE. 2. EX - EXIT. btw, the exit is right next to number 16, but the picture didn't fit. The guard said that you will be free if you enter every cell of your friends [ the red lines are entrances and exits for other cells ] only ONE time. So you have to go through every cell of your friends only once and reach the exit.
SOLUTION:
OK, didn't work? If you read the text carefully, you could see that you have to enter only once the cells of your friends... but that means that you can enter your cell more times! So how to do it. From cell 1 go to cell 2, then return to cell 1, then to cell 5, then to cell 6, then to cell 7 then to cell 3, then to cell 4, then to cell 8, 12, 11, 10, 9, 13, 14, 15, 16... and you are free!