some TrIckY puzzles

1.Boston United's latest player lives on the 13th floor of a tower block. Every morning he takes the lift down to the ground floor and leaves the building. When he returns home in the evening, if there is someone else in the lift or it's raining he goes straight back to his floor directly. However, if there is nobody else in the lift or it hasn't rained he goes up to the 10th floor and walks up the remaining three flights of stairs. He hates walking up stairs so why does he do it?

2.There are 2 identical strings. If you light one of the strings at its end, it will take exactly one hour for it to finish burning completely. The string will not burn evenly - it is thicker in some places, thinner in others. For example, the string may not be half consumed exactly 30 minutes from lighting it at one end. You have no other means of telling time, and you want to know when exactly 45 minutes have passed. All that you have is a lighter and these 2 identical strings. What is the most accurate method you can use, given these conditions?

3.A water lily growing in a circular pond doubles in size every day. It takes thirty days to cover the whole pond. How long does it take to cover half the pond?