Simple Probability and its Complement

​Simple Probability and its Complement

By Isabel Pawling

Open Ended

Review:
1. In your own words, what is probabilty?
2. Describe an event that is not likely (but not impossible).
3. Describe an event that is likely (but not certain).

What is simple probability?

Simple Probability

Simple probability is the most basic form of probability.
Simple probability describes the likelihood of a single event happening when all possible outcomes are equally likely.
Probability can be described using a ratio (fraction), decimal or percent.

How do we calculate simple probability?

​The probability of an event is calculated using the formula:







Favorable outcomes: the results you want, the desired outcome

Total outcomes: ALL the possible results (outcomes) that could happen

Note: Probability can be written as a fraction (in simplest form), a decimal or a percent.

Example 1:

Multiple Choice

What is the probability of the spinner landing on red?

• 5/12
• 7/12

• 5/5
• 5/10 or 1/2

Multiple Choice

What is the probability of landing on the color blue on the spinner?

• 3/3
• 1

• 3/12 or 1/4
• 3/9 or 1/3

Multiple Choice

What is the probability of spinning green?

• 0
• 1/4
• 1/2
• 3/4

Example 2:

Multiple Choice

A die is rolled. What is the probability that the result is less than 3 ?

• 1/2
• 1/3
• 1/4
• 1/6

Multiple Choice

Find the probability of rolling a number greater than a 1 on a number cube.

• 6/6
• 5/6
• 4/6
• 1/6

Here are some more simple probability practice questions.
Remember to simplify your fractions!

Multiple Choice

• 1/2

• 1/3,

• 2/3

• 1/5

Multiple Choice

• 0%

• 1/6

• 1/2

• 6/6

Multiple Choice

• 0%

• 1/4

• 1/2

• 100%

Multiple Choice

• 1/5

• 4/5

• 2/3

• 0%

Multiple Choice

• 2/9

• 5/9

• 1/9

• 7/9

Multiple Choice

10 M&Ms are in a bag, 4 red, 2 blue, 1 green and 3 brown. What is the probability of pulling out a blue candy?

• 1

• 2/10

• 1/5

• 3/10

Multiple Choice

You pick a marble from this bag.

What is the probability you will choose either a solid black or a solid white marble?

• 3/5

• 9/100

• 1/10

• 2/5

Complement

​In probability, what does the complement represent?

The complement of an event is “everything that does not happen.”
If an event is called A, then the complement of A means:

All the outcomes where A does NOT happen.

​P(odd) = probability the outcome is odd

​What is the probability of rolling an odd number on a number cube?

P′(odd) = probability the outcome is NOT odd

​What is the probability of NOT rolling an odd number on a number cube?

You can write the complement three different ways:
P′(odd) = P(odd′) = P(not odd)

​In probability, the little prime symbol ′ (apostrophe) means “complement.”

​How do we write the complement in probability?

​P(event) + P′(event) = 1

In probability ....

Multiple Choice

What is a Complement in probability?

• Saying "You look very nice today"

• Probability of an event happening

• Probability of an event NOT happening

• An angle less than 90 degrees

Multiple Choice

A bag of candy contains 2 red, 4 yellow, and 4 green candies.

Find: P(NOT red or yellow)

• 3/5

• 1/5

• 2/5

• 4/5

Multiple Choice

P'(even) =

• 5/7

• 1/7

• 2/7

• 4/7

Multiple Choice

There are 14 girls and 12 boys in a class.

P(boy') =

• 7/13

• 6/13

• 4/13

• 12/25

Multiple Choice

Given the pie chart shown:

Find P'(hearts, dots, or stars) =

• 2 out of 3

• 3 out of 8

• 5 out of 8

• 1 out of 3

Multiple Choice

A bag contains 5 quarters, 2 dimes, and 4 pennies. Find: P(Penny') =

• 5/11

• 5/6

• 1/3

• 7/11

Open Ended

The probability that a 6th grade student will choose a non-fiction book while visiting the library is 2/5.
What does the fraction 3/5 represent in this situation?

Open Ended

Why is probability useful in sports?

Can you think of a time when knowing chances helped a coach or player?

Open Ended

Summarize this lesson in 2 to 3 sentences.

Open Ended

Finally ....

What is P'(school closing on Monday) =

(If we have no school on Monday ... what will you do on your day off?)

The End ... Well Done!!!