Good Riddles

Question: In 1940, a correspondent proposed the following question:

A man's age at death was one twenty-ninth of the year of his birth. How old was he in 1900?

Question: Different lights make me strange,
for each one my size will change.

What am I?

Question: Suppose you had to pick 1 of 3 doors to go through. One has ninja assassins, one has a lion that hasn't eaten in 3 months, and one has a flaming inferno. Which door should you choose in order to live?

Question: There are 100 coins scattered in a dark room. 90 have heads facing up and 10 are facing tails up. You cannot tell which coins are which. How do you sort the coins into two piles that contain the same number of tails up coins?

Question: I can be used to build castles,
but I crumble in your hands.
I can help a man see,
and am found all around the lands.

What am I?