Probability with AND

Question

You are going to draw two candy bars from a large bag containing 30 Snickers bars and 9 Twix bars. What is the probability that the first draw is a Snickers and the second draw from the bag is a Twix?

 

Calculate the probability.

(Round to three decimal places.)

Answer 1

There are 39 candy bars altogether.

 

First consider the first draw:  There are 30 Snickers bars, so the probability that the first draw is Snickers is 30/39 = 10/13.

 

After the first draw, there are only 38 left.  How many of each?  Well you have to assume that the first one was a Snickers, because if it wasn't, it wouldn't matter what the second draw was -- you'd already fail the conditions of the problem!  So there still have to be 9 Twix left.  So the probability of the second one being Twix is 9/38.

 

So the probability of BOTH events happening is 10/13 * 9/38 = 0.182.