# Probability and Counting

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1. The chance something will happen.
Probability
2. Sue has 3 purple marbles, 5 red marbles, and 4 yellow marbles on the floor. Her cat comes along and bats one marble under the chair. What is the probability it is a purple marble?
• 3/12 = 1/4
• The number of purple marbles, 3, will be on the top of the fraction. The total number of marbles, 12, will be on the bottom of the fraction.
3. Determine the probability that the pointer will stop on an odd number if the spinner has 7 sections numbered 1-7.
• 4/7
• Four odd numbers over a total of 7.
4. A computer chooses a random number between 1 and 50. What is the probability of you guessing the same number that the computer chooses in 1 try? Then write the number as a percent.
1/50 = 2%
5. Julie tosses a coin 4 times. What is the probability she gets all tails?
1/2 x 1/2 x 1/2 x 1/2 = 1/16
6. Consider the set B = { -100, -56, -32, 1, 39, 85, 213}. How many ways are there to choose a negative OR odd number?
7
7. Omar goes to a fast food restaurant for lunch. There are 5 sandwiches and 4 sides to choose from. He wants to pick one sandwhich and one side. How many different meals can be order?
5 x 4 = 20
8. Joseph needs to choose a password for his email account. It must be 8 characters long. Four of the characters must be numbers and four of the characters must be letters. How many different password choices does he have?
• There are 10 numbers, so there are 10 choices for the first four characters of the password. There are 26 letters, so there are 26 choices for the next four characters of the password.
• 10 x 10 x 10 x 10 x 26 x 26 x 26 x 26 = 4, 569, 760, 000
9. How many different ways could you choose a number from 1 to 30 so that it is a multiple of 5 or 8?
9

• Multiples of 5: 5 10 15 20 25 30
• Multiples of 8: 8 16 24
 Author: AChuppTeaches ID: 77681 Card Set: Probability and Counting Updated: 2011-04-06T02:46:21Z Folders: Description: 8th Grade CRCT Prep Show Answers: