Gyou have two coins, one of which is fair and comes up heads with a probability 1/2, and the other which is biased and comes up heads with probability 3/4. you randomly pick coin and flip it twice, and get heads both times. what is the probability that you picked the fair coin?

There are many benefits to using folders when working with lots of files.  Here are a few examples:

- You can use folders to sort your files by type, almost like drawers in a desk, so you might have folders for Music, Photographs, Documents, etc.

- You can use folders to group files together into a specific group.  For example in your Photographs folder you might have a folder titled BirthdayPhotographs for all the photographs from your birthday.

- As in the example above you can nest folders to create sub-categories.  Documents might include folders for Homework, Stories, Poems

- Folders can have different permissions applied to them, allowing you to keep personal files in a private folder only you can access, or secret files in a folder that doesn't show up in the normal list of folders!