Brain Teaser's

1. There is a man who lives on the top floor of a very tall building. Everyday he gets the elevator down to the ground floor to leave the building to go to work. Upon returning from work though, he can only travel half way up in the lift and has to walk the rest of the way unless it's raining! Why?
2. Find the next number 1,11,21,1211,111221,312211,...............
3. One day Emile celebrated her birthday. A day later her older twin brother, Edward, celebrated his birthday. How?
4. A woman had two sons who were born on the same hour of the same day of the same year. But they were not twins. How could this be so?
5.  Jack tore out several successive pages from a book. The number of the first page he tore out was 183, and it is known that the number of the last page is written with the same digits in some order. How many pages\did Jack tear out of the book?
6. Peter said "The day before yesterday I was 10 but I will turn 13 next year". Is this possible?
7. You are in the downstairs lobby of a house. There are three switches. aall in the “off” position. Upstairs, there is a room with a light bulb that is turned off. One and only one of the three switches controls the bulb. You want to discover which switch controls the bulb, but you are only allowed to go upstairs once. How do you do it?
8. Ten saplings are to be planted in straight lines in such way that each line has exactly four of them. 
9. A bear walks south for one kilometer, then it walks west for one kilometer, then it walks north for one kilometer and ends up at the same point from which it started ? How is this possible ? How many point's are there on earth on which this is possible?
10. I have two rectangular bars.They have property such that when you light the fire from one end , it will take exactly 60 seconds to get completely burn.However they do not burn at consistent speed (i.e it might be possible that 40 percent burn in 55 seconds and next 60 percent can burn in 10 seconds).How do you measure 45 seconds ? 
11. You are in a strange place which is guarded by two guards.One of the guard always say truth while other always lies.You don't know the identity of the two.You can ask only one question to go out from there. What should you ask?