CK-12 Basic Probability and Statistics - A Short Course

http://www.ck12.org Chapter 3. Discrete Random Variables - Basic

#o f favorable choices=

#possible letters in combination!

letter X!×letter Y!

#o f favorable choices=

4 letters!

1 head!× 3 tails!

#o f favorable choices=

4 × 3 × 2 × 1

1 ×( 3 × 2 × 1 )

#o f favorable choices=

24

6

#o f favorable choices= 4

Denominator (Bottom)

The number of possible outcomes= 2 × 2 × 2 × 2 = 16

We now want to find the number of possible times we could get one head when we do these four tosses (or our
favorable outcomes).

Remember:

Possible outcomes= 2 nwheren=number of tosses.

Here we have 4 tosses. Therefore,

Possible outcomes= 2 n

Possible outcomes= 24

Possible outcomes= 2 × 2 × 2 × 2

Possible outcomes= 16

Now we just divide the numerator by the denominator.

P( 1 head) =

4

16

P( 1 head) =

1

4

Technology Note:

Let’s take a look at how we can do this using the TI-84 calculators. There is an application on the TI calculators
called the coin toss. Among others (including the dice roll, spinners, and picking random numbers), the coin toss is
an excellent application for when you what to find the probabilities for a coin tossed more than 4 times or more than
one coin being tossed multiple times.

Let’s say you want to see one coin being tossed one time. Here is what the calculator will show and the key strokes
to get to this toss.