Simple puzzles

The Birthday Problem
The birthday problem asks how many people you need to have at a party so that there is a better-than-even chance that two of them will share the same birthday

The Children Puzzle
I tell you that a couple has two children and that (at least) one of them is a boy. I ask you what is the probability that their other child is a boy.

for solutions refer to

http://www.npr.org/templates/story/story.php?storyId=4542341

A Quick Teaser

Each child in a family has at least 5 brothers and 4 sisters. What is the smallest number of children the family might have?