http://www.ck12.org Chapter 3. Discrete Random Variables - Basic
If our first toss were a heads...
If our first toss were a tails...
Therefore the possible outcomes are:
HHH,HHT,HTH,HTT,THH,THT,TTH,TTT
P(1 head) =3
8
Alternate Solution:
We have one coin and want to find the probability of getting one head in three tosses. We need to calculate two parts
to solve the probability problem.
Numerator (Top)
In our example, we want to have 1 H and 2Ts. Our favorable outcomes would be any combination of HTT. The
number of favorable choices would be:
#o f favorable choices=#possible letters in combination!
letter X!×letter Y!
#o f favorable choices=
3 letters!
1 head!× 2 tails!
#o f favorable choices=3 × 2 × 1
1 ×( 2 × 1 )
#o f favorable choices=6
2
= 3
Denominator (Bottom)
The number of possible outcomes= 2 × 2 × 2 = 8
We now want to find the number of possible times we could get one head when we do these three tosses. We
call these favorable outcomes. Why? Because these are the outcomes that we want to happen, therefore they are
favorable.