7th Grade Math

Everyday Use

Independent not under

control by others

Math Use

Independent outcome

does not rely on another

event

A spinner and a number cube are

GREEN

RED

YELLOWBLUE

PURPLE

are used in a game. The spinner

has an equal chance of landing

on one of five colors: red, yellow,

blue, green, or purple. The faces

of the cube are labeled 1 through

6. What is the probability of a
   player spinning blue and then
   rolling a 3 or 4?

You are asked to find the probability of the spinner landing on

blue and rolling a 3 or 4 on a number cube. The events are

independent because spinning the spinner does not affect the

outcome of rolling a number cube.

First, find the probability of each event.

P(blue) = _^1

5

___number of ways to spin blue

number of possible outcomes

P(3 or 4) = _ 62 or_^13

___number of ways to roll 3 or 4

number of possible outcomes

Then, find the probability of both events occurring.

P(blue and 3 or 4) = _ 51 · _^13 P(A and B) = P(A) · P(B)

= _ 151 Multiply.

The probability is _ 151.

a. A game requires players to roll two number cubes to move the

game pieces. The faces of the cubes are labeled 1 through 6.

What is the probability of rolling a 2 or 4 on the first number

cube and then rolling a 5 on the second?

If the outcome of one event affects the outcome of another event, the

events are called dependent events.

Probability of Dependent Events

Words If two events A and B are dependent, then the probability

of both events occurring is the product of the probability of

A and the probability of B after A occurs.

Symbols P(A and B) = P(A) · P(B following A)

Lesson 2B Compound Events 451

Everyday Use

Dependent under the

control of others

Math Use

Dependent relying on

another quantity or action

449_455_C08_L2_895130.indd 451 12/29/09 1:26 PM