Brain Teasers

1. Girl or Boy?
Teanchi and Beanchi are a married couple with two children.  One of them is a girl. What is the probability that the other one is also a girl?

2. Fly Logic Puzzle
Two trains, 200 km apart, are moving toward each other at the speed of 50 km/hour each. Just as they begin their simultaneous journey, a fly takes off from one train flying straight toward the other at the speed of 75 km/hour. Having reached the other train, the fly bounces off it and flies back to the first train. The fly repeats the trip until the trains collide and the bug is squashed.  What distance has the fly travelled until its death?

3. Sequence Puzzle
Below is a number puzzle. It should be read left to right, top to bottom. The first five rows are filled.

       1
      1 1
      2 1
    1 2 1 1
  1 1 1 2 2 1
  ? ? ? ? ? ?
? ? ? ? ? ? ? ?

Can you fill the next two rows of numbers? How did you get this answer?

From brainden.com