Statistics 1 Week 7

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Probability Summary

What is Probability?

Probability is a branch of mathematics that deals with the likelihood or chance of different outcomes. It quantifies uncertainty and helps in making predictions about future events based on known data. Probability is used to measure how likely an event is to occur, expressed as a number between 0 and 1. A probability of 0 means the event will not happen, while a probability of 1 means the event will certainly happen.

Use of Probability

Probability is used in various fields such as finance, insurance, medicine, and everyday decision-making. In finance, it helps in assessing the risk of investments. In insurance, it is used to calculate premiums based on the likelihood of claims. In medicine, probability is used in clinical trials to determine the effectiveness of treatments. In everyday life, we use probability to make decisions like whether to carry an umbrella based on the weather forecast.

Need of Probability

Probability is essential for making informed decisions in uncertain situations. It provides a framework for analyzing random events and helps in predicting the likelihood of different outcomes. Without probability, we would have no systematic way to deal with uncertainty and risk. It allows us to quantify uncertainty and make decisions based on the likelihood of various outcomes.

Experiment and Random Experiment

An experiment is a procedure that produces observable results. A random experiment is one where the outcome is not predictable with certainty. For example, tossing a coin or rolling a die are random experiments because the outcome cannot be predicted with certainty. Each time the experiment is performed, it may produce a different result.

Favorable Outcome and Total Outcome

A favorable outcome is an outcome that satisfies the condition of an event. For example, if we are interested in the event of rolling a 4 on a die, then rolling a 4 is a favorable outcome. The total outcome is the set of all possible outcomes of an experiment. For example, the total outcomes for rolling a die are 1, 2, 3, 4, 5, and 6.

Sample Space

The sample space is the set of all possible outcomes of a random experiment. For example, the sample space for tossing a coin is {Heads, Tails}. The sample space for rolling a die is {1, 2, 3, 4, 5, 6}. The sample space provides a complete list of all possible outcomes of an experiment.

Set Notation

In order to understand probability, set notation has to be clear. A set is a collection of distinct objects. The union of sets is the set containing all elements from both sets. The intersection of sets is the set containing only the elements common to both sets. The complement of a set is the set of all elements not in the original set. For example, if A is the set of even numbers and B is the set of numbers greater than 5, then the union of A and B is the set of all even numbers and numbers greater than 5.

Formula to Find Union

The formula to find the union of two sets A and B is given by: P(A ∪ B) = P(A) + P(B) - P(A ∩ B). This formula accounts for the fact that the intersection of A and B is counted twice when we add P(A) and P(B), so we subtract it once to get the correct probability of the union.

Range of Probability

The range of probability is between 0 and 1, inclusive. A probability of 0 means the event is impossible, while a probability of 1 means the event is certain. Probabilities cannot be negative or greater than 1 because they represent proportions of the total possible outcomes.

Why Probability is Always Between 0 and 1

Probability is always between 0 and 1 because it represents a proportion of the total possible outcomes. It cannot be negative or greater than 1 as it would not make sense in the context of likelihood. For example, if an event has a probability of 0.5, it means that the event is expected to occur half of the time in the long run.

Null Set and Null Event

A null set is a set with no elements. A null event, or disjoint event, is an event that cannot occur. For example, rolling a 7 on a standard six-sided die is a null event because it is impossible. Null events are important in probability because they help us understand the concept of mutually exclusive events, which cannot happen at the same time.

Complement of an Event

The complement of an event is the set of all outcomes in the sample space that are not part of the event. For example, if the event is rolling a 3 on a die, the complement is rolling a 1, 2, 4, 5, or 6. The probability of the complement of an event is 1 minus the probability of the event.

Equally Likely Outcomes

Equally likely outcomes are outcomes that have the same probability of occurring. For example, in a fair coin toss, the outcomes Heads and Tails are equally likely because each has a probability of 0.5. In a fair die roll, each of the six faces has an equal probability of 1/6.