Carcass wrote:
A magician has five animals in his magic hat: 3 doves and 2 rabbits. If he pulls two animals out of the hat at random, what is the chance that he will have a matched pair?
A. 2/5
B. 3/5
C. 1/5
D. 1/2
E. 7/5
One approach is to solve the question using 
counting methodsTo begin, P(matched pair) = (
# of ways to get a matched pair)/(
# of ways to select 2 animals)
As always, begin with the 
denominator. 
# of ways to select 2 animalsTo count this, we'll treat each animal as different. 
We'll take the task of selecting 2 animals and break it into stages. 
Stage 1: Select the 1st animal. There are 5 animals, so this stage can be accomplished in 5 ways. 
Stage 2: Select the 2nd animal. There are now 4 animals remaining, so this stage can be accomplished in 4 ways.
So, the total number of ways to select 2 animals is (5)(4), which equals 
20Now the 
numerator.
 # of ways to get a matched pair
We need to consider two cases. 
Case 1: select 2 doves. 
In how many different ways can this occur? 
Well, we'll take the task of selecting 2 doves and break it into stages. 
Stage 1: Select the 1st dove. There are 3 doves, so this stage can be accomplished in 3 ways. 
Stage 2: Select the 2nd dove. There are now 2 doves remaining, so this stage can be accomplished in 2 ways.
So, the total number of ways to select 2 doves is (3)(2), which equals 
6Case 2: select 2 rabbits. 
In how many different ways can this occur? 
Well, we'll take the task of selecting 2 rabbits and break it into stages. 
Stage 1: Select the 1st rabbit. There are 2 rabbits, so this stage can be accomplished in 2 ways. 
Stage 2: Select the 2nd rabbit. There is now 1 rabbit remaining, so this stage can be accomplished in 1 ways.
So, the TOTAL number of ways to select 2 rabbits is (2)(1), which equals 
2Put it all together to get: 
P(matched pair) = (
6+2)/(
20)
= 
8/
20= 2/5 
= A
Cheers, 
Brent