7th Grade Math

460 Probability and Predictions

Theoretical and experimental probability can be used to make

predictions about future events.

Predict Future Events

MEDIA Last year’s sales at the Buy More

DVD Store are shown. What is the

probability that a customer bought

a comedy DVD last year?

2,000 DVDs were sold and 580 were

comedy. So, the probability is _2,000^580 or _ 10029.

Suppose a media buyer expects to sell 5,000 DVDs this year.

How many comedy DVDs should she buy?

_2,000^580 = _5,000x Write a proportion.

580 · 5,000 = 2,000 · x Find the cross products.

2,900,000 = 2,000x Multiply.

1,450 = x Divide each side by 2,000.

She should buy about 1,450 comedy DVDs.

d. What is the probability that a person buys a horror DVD?

e. If the media buyer expects to sell 3,000 DVDs this year, about

how many action movies should she buy?

Muffin of PeopleNumber

Blueberry 22

Poppyseed 17

Banana 11

Examples 1–3 11 A coin is tossed 50 times, and it lands on heads 28 times.

a. Find the experimental probability of the coin landing on heads.

b. Find the theoretical probability of the coin landing on heads.

c. Compare the probabilities in Exercises a and b.

Examples 4 and 5 2. FOOD The table shows the types of muffins

that customers bought one morning from a bakery.

a. What is the probability that a customer bought

a blueberry muffin?

b. If 100 customers buy muffins tomorrow, about

how many would you expect to buy a banana

muffin?

DVDs Sold

Type Number

Action 670

Comedy 580

Drama 450

Horror 300

Solving Proportions

The cross products of any

proportion are equal.

450 x

=

2,000 5,000

450 · 5,000 = 2,000 · x

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