7th Grade Math

452 Probability and Predictions

FRUIT There are 4 oranges,

7 bananas, and 5 apples in a

fruit basket. Ignacio selects

a piece of fruit at random and

then Terrance selects a piece

of fruit at random. Find the

probability that two apples

are chosen.

Since the first piece of fruit is not replaced, the first event affects

the second event. These are dependent events.

P(first piece is an apple) = _ 165

number of apples

total pieces of fruit

P(second piece is an apple) = _ 154

number of apples left

total pieces of fruit left

1 1

P(two apples) =

5

_

16

·

4

_

15

or _ 121

4 3

The probability that two apples are chosen is _ 121.

Refer to the situation above. Find each probability.

b. P(two bananas) c. P(orange then apple)

d. P(apple then banana) e. P(two oranges)

Replacement Replacement

When finding the

probability of an event,

“with replacement” means

to put the first piece of

fruit chosen back into the

basket before choosing

the second piece. “Without

replacement” means to

choose the second piece

of fruit without putting the

first piece back in the

basket.

Example 1 A penny is tossed and a number cube is rolled. Find each probability.

11 P(tails and 3) 2. P(heads and odd)

Example 2 3. A spinner and a number cube are used in a game. The spinner has an

equal chance of landing on 1 of 3 colors: red, yellow, and blue. The faces

of the cube are labeled 1 through 6. What is the probability of a player

spinning red and then rolling an even number?

A card is drawn at random from the cards

shown and not replaced. Then, a second card

is drawn at random. Find each probability.

Example 3

4. P(two even numbers)


5. P(a number less than 4 and then a
   number greater than 4)

449_455_C08_L2_895130.indd 452 12/29/09 1:27 PM