7th Grade Math

You can use the Fundamental Counting Principle to find the

probability of an event.

Find Probability

SWIMMING The finals of the Northwest Northwest League

Finalists

Octavia Eden

Natasha Paquita

Calista Samantha

Yumii Lorena

Swimming League features 8 swimmers.

If each swimmer has an equally likely

chance of finishing in the top two, what

is the probability that Yumii will be in

first place and Paquita in second place?

There are 8 choices for first place.

There are 7 choices that remain for second place.

the number of permutations of the two places

There are 56 possible arrangements, or permutations, of the

two places.

Since there is only one way of having Yumii come in first and

Paquita second, the probability of this event is _ 561.

b. LETTERS Two different letters are randomly selected from the

letters in the word math. What is the probability that the first

letter selected is m and the second letter is h?

Example 1 1. AMUSEMENT PARKS Seven friends

are waiting to ride the new roller

coaster. In how many ways can

they board the ride, once it is

their turn?

2. COMMITTEES In how many ways
   can a president, vice president,
   and secretary be randomly selected
   from a class of 25 students?
   Example 2 33 DVDs You have five seasons of your favorite TV show on DVD. If you
   randomly select two of them from a shelf, what is the probability that
   you will select season one first and season two second?


3. PASSWORDS A password consists of four letters, none of which are
   repeated. What is the probability that a person could guess the entire
   password by randomly selecting the four letters?

d

f it TV h DVD If

Lesson 1D Probability 445

Reasonable Answers A

possible probability of _ 561

indicates that it is unlikely

that Yumii will finish first

and Paquita will finish

second.

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440_447_C08_L1_895130.indd 445 12/29/09 1:18 PM