Probability Problem

Date: 4 Jun 1995 12:15:53 -0400
From: Anonymous
Subject: Probability

6th grade math problem:  There's a box with 12 letters, one of which is a D,
and 2 are E's.  I know that the probability of getting a D is therefore 1 out
of 12, and an E is 1 out of 6.  However, how do I determine the probability
of getting a D and then an E, if the D is replaced after being selected?

Date: 6 Jun 1995 12:28:53 -0400
From: Dr. Ken
Subject: Re: probability

Hello there!

You can find out how many different favorable possibilities there are for
drawing, and then divide that by the total number of possibilities for
drawing.  In this case, there are 2 different ways you can get a D and then
an E.  You can draw the D and then the first E, or you can draw the D and
then the other E.  

Now how many different ways are there you can draw 2 letters from the bag?
Well, since there are 12 possibilities for each draw, there are 12x12 = 144
possibilities.  So the probability we get a D and then an E is 2/144, or 
1 out of 72.  Thanks for the question!

-Ken