4-2 Probability Explained
Key Concepts
1. **Probability**: The likelihood or chance of an event occurring.
2. **Sample Space**: The set of all possible outcomes of an experiment.
3. **Event**: A specific outcome or set of outcomes of an experiment.
4. **Probability Formula**: The formula to calculate the probability of an event is \( P(E) = \frac{\text{Number of favorable outcomes}}{\text{Total number of possible outcomes}} \).
Detailed Explanation
Probability
Probability measures how likely an event is to occur. It is expressed as a number between 0 and 1, where 0 means the event will not occur, and 1 means the event is certain to occur. For example, the probability of flipping a coin and getting heads is 0.5.
Sample Space
The sample space is the set of all possible outcomes of an experiment. For example, when rolling a six-sided die, the sample space is {1, 2, 3, 4, 5, 6}.
Event
An event is a specific outcome or set of outcomes of an experiment. For example, in rolling a die, the event "rolling an even number" includes the outcomes {2, 4, 6}.
Probability Formula
The probability of an event \( E \) occurring is calculated using the formula:
\[ P(E) = \frac{\text{Number of favorable outcomes}}{\text{Total number of possible outcomes}} \]
For example, the probability of rolling a 3 on a six-sided die is \( \frac{1}{6} \).
Examples
Example 1: Calculate the probability of drawing a red card from a standard deck of 52 cards.
Solution: There are 26 red cards in a deck of 52 cards.
\[ P(\text{Red card}) = \frac{26}{52} = \frac{1}{2} = 0.5 \]
Explanation: The probability of drawing a red card is 0.5 or 50%.
Example 2: Calculate the probability of rolling a sum of 7 with two six-sided dice.
Solution: The sample space for two dice is 36 possible outcomes. The favorable outcomes for a sum of 7 are (1,6), (2,5), (3,4), (4,3), (5,2), and (6,1).
\[ P(\text{Sum of 7}) = \frac{6}{36} = \frac{1}{6} \approx 0.167 \]
Explanation: The probability of rolling a sum of 7 is approximately 0.167 or 16.7%.
Analogies
Think of probability as the chance of finding a specific toy in a box of mixed toys. The sample space is all the toys in the box, and the event is finding the specific toy you want. The probability formula helps you determine how likely it is to find that toy.
Practical Application
Understanding probability is crucial in various fields such as statistics, finance, and risk management. It helps in making informed decisions, predicting outcomes, and analyzing uncertainties.