Probability ideas

Probabilities are measured with numbers between 0 and 1, or percents between 0 and 100.

If the probability of something happening is measured by the number P, then the probability of it not happening is 1-P

Figuring out the probability of something happening is a matter of making a ratio of (ways it can happen)/(equally likely things that can happen.

Figuring out the probability for what can happen with two dice or two spinners is something you can do by using a grid.

Study questions

1. I have two 10-sided dice, numbered 1-10. If I toss both of them, what is the probability that I will get

• a sum that is an even number?
• a sum that is over 10?
• a sum that is equal to 10?
• doubles

2. I have a 10-sided die and a 6-sided die. If I toss them both, what is the probability that I will get:

• a sum that is at least 12?
• a sum that is over 10?
• a sum that is equal to 10?
• double

3. I have two funny spotted 6-sided dice. Die A has the numbers: 1, 1, 3, 3, 5, 6 and die B has the numbers 2, 2, 2, 4, 4, 4.

• Which die (if any) will be larger most often?
• What is the probability that the first die will be bigger than the second?

4. Josh, Sarah, Kelly and Brian had these dice:

Josh: 2, 2, 2, 2, 6, 6
Sarah:3, 3, 3, 3, 3, 3
Kelly: 4, 4, 4, 4, 0, 0
Brian: 1, 1, 1, 5, 5, 5

A. If Josh and Sarah both roll their dice, who will have the higher number more often?

B. If Sarah and Kelly both roll their dice, who will have the higher number more often?

C. If Kelly and Brian both roll their dice, who will have the higher number more often?

D. If Brian and Josh both roll their dice, who will have the higher number more often?

Answers