Basics
Probability is the chance that an event will occur.
Probability can be expressed as a fraction, decimal, or percent.
Probability of Simple Event =
• The TI30XS MultiView Scientific Calculator may or may not be needed here.
• Calculator Not Needed: Probability of rolling a five on a single die =
• Calculator Needed: Probability of picking 12 orange balls out of a total of 100 balls, the rest of which are not orange = =
• When asked to convert a fraction to decimal form, use the toggle button .
Probability of Compound Event = Probability of Multiple Events
• The calculator is usually needed here.
• To arrive at the answer, multiply the probabilities.
• When fractions are multiplied, the answer will be in fraction form.
> Probability of rolling 1 followed by 2 with a die = × =
• When percents are multiplied, the answer will be in decimal form.
> Probability of snow 40% on Monday followed by 60% on Tuesday = 40% × 60% = 0.24
• When asked to convert a decimal to percent frome, move the decimal point two places to the right.
> 0.24 = 24.% = 24%
Formulas (NOT on Mathematics Formula Sheet)
Probability of Simple Event =
Probability of Compound Event = Probability of Multiple Events
Question
When rolling a single die from a pair of dice, there are six possible outcomes: 1 or 2 or 3 or 4 or 5 or 6. In fractional terms, when a die is rolled, what is the probability of a 2?
Answer
Answer Process
What is the probability of a simple event?
What is the probability of one out of six possible events?
Calculator not needed.
Question
In fractional terms, what is the probability of picking 24 orange balls out of a total of 100 balls, the rest of which are not orange?
Answer
Answer Process
What is the probability of a simple event?
What is the probability of 24 out of 100 possible events?
Calculator needed.
Input  Display  Comment 
blinker  clears screen  
24 100  Simple Event  
Answer  
Probability 
Question
With reference to the question above, express your answer in decimal form.
Answer
0.24
Answer Process
See Toggle.
⇔ 0.24
Input  Display  Comment 
blinker  clears screen  
24 100  Simple Event  
0.24  Answer (Toggle) 

Probability 
Question
With reference to the question above, express your answer in percent form.
Answer
24%
Answer Process
See Percent.
To convert a decimal to percent, move the decimal point two places to the right.
0.24 = 24.% = 24%
Question
When rolling a single die from a pair of dice, there are six possible outcomes: 1 or 2 or 3 or 4 or 5 or 6. In fractional terms, when a die is rolled, what is the probability of rolling a 2 followed by 5?
Answer
Answer Process
What is the probability of a compound event?
Multiply the probabilities.
× =
Input  Display  Comment 
blinker  clears screen  
1 6 × 1 6 
*  Compound Event 
Answer  
Probability 
Question
With reference to the question above, express your answer in decimal form.
Answer
0.027777778
Answer Process
See Toggle.
⇔ 0.027777778
Input  Display  Comment 
blinker  clears screen  
1 6 × 1 6 
*  Compound Event 
0.027777778  Answer (Toggle) 

Probability 
Question
With reference to the question above, express your answer in percent form.
Answer
2.777777778%
Answer Process
See Percent.
To convert a decimal to percent, move the decimal point two places to the right.
0.027777778 = 2.7777778%
Question
With reference to the question above, round your answer to the nearest hundredth.
Answer
2.78%
Answer Process
See Rounding.
2.7777778% → 2.78%
Question
The probability of snow is 65% on Friday, 75% on Saturday, 55% on Sunday, and 85% on Monday. In percent terms, rounded to the nearest tenth, what is the probability of snow on all four days?
Answer
22.8%
Answer Process
What is the probability of a compound event?
Multiply the probabilities.
65% × 75% × 55% × 85% = 0.22790625
To convert a decimal to percent, move the decimal point two places to the right.
0.22790625 = 22.790625% (See Percent.)
Round to the nearest tenth.
22.790625% → 22.8% (See Rounding.)
Input  Display  Comment 
blinker  clears screen  
65 × 75 × 55 × 85 × 
65%*75%*55%*85%  Compound Event 
0.22790625  Answer (before percent and rounding) 

Probability 
Practice – Questions
1. When flipping a coin, there are two possible outcomes: heads or tails. In fractional terms, when a coin is flipped, what is the probability of flipping heads?
2. When flipping a coin, there are two possible outcomes: heads or tails. In fractional terms, when a coin is flipped, what is the probability of flipping tails?
3. When flipping a coin, there are two possible outcomes: heads or tails. In fractional terms, when a coin is flipped, what is the probability of flipping heads followed by heads?
4. When flipping a coin, there are two possible outcomes: heads or tails. In fractional terms, when a coin is flipped, what is the probability of flipping tails followed by tails?
5. When flipping a coin, there are two possible outcomes: heads or tails. In fractional terms, when a coin is flipped, what is the probability of flipping heads followed by tails?
6. When flipping a coin, there are two possible outcomes: heads or tails. In fractional terms, when a coin is flipped, what is the probability of flipping tails followed by heads?
7. When flipping a coin, there are two possible outcomes: heads or tails. In decimal terms, when a coin is flipped, what is the probability of flipping heads followed by tails?
8. When flipping a coin, there are two possible outcomes: heads or tails. In percent terms, when a coin is flipped, what is the probability of flipping heads followed by tails?
9. When flipping a coin, there are two possible outcomes: heads or tails. In percent terms, rounded to the nearest tenth, when a coin is flipped, what is the probability of flipping heads followed by heads followed by heads followed by heads?
10. The probability of precipitation is 55% on Friday, 65% on Saturday, and 45% on Sunday. In percent terms, rounded to the nearest hundredth, what is the probability of precipitation on all three days?
Practice – Answers
1.
2.
3.
4.
5.
6.
7. 0.25
8. 25%
9. 6.3%
10. 16.09%