Question

Let \(x\) be a binomial random variable with \(n=7\) and \(p=.5 .\) Find the values of the quantities in Exercises \(11-15 .\) $$ \mu=n p $$

Short answer

Answer: The mean is 3.5.

Step-by-step solution

Identify the formula for the mean of a binomial distribution

We are given a binomial random variable \(x\) and the formula for the mean of a binomial distribution is \(\mu = np\).

Substitute the given values for n and p into the formula

To find \(\mu\), we will substitute the values for \(n\) and \(p\) into the formula: \(\mu = np = 7 \times 0.5\).

Calculate the mean of the binomial distribution

Now we can calculate \(\mu\): \(\mu = 7 \times 0.5 = 3.5\). The mean of the binomial random variable with \(n=7\) and \(p=0.5\) is \(3.5\).

Key concepts

Understanding Probability Theory

Probability theory is the branch of mathematics that deals with the analysis of random phenomena. It forms the foundation for various statistical methods and helps us quantify the likelihood of certain events occurring. For instance, if we flip a coin, probability theory allows us to calculate that there is a 50% chance of getting heads or tails—a fundamental concept for the binomial distribution.

In probability theory, we use a probability value, denoted by the letter ‘p,’ to represent the chance of a particular outcome. This value ranges from 0 to 1, where 0 indicates impossibility and 1 indicates certainty. Taking the coin flip example further, the probability of a fair coin landing on heads (p) is 0.5, or 50%.

Understanding this theory is crucial because it enables us to make predictions and informed decisions based on the likelihood of various outcomes. In statistical terms, these predictions often relate to the characteristics of probability distributions, such as the mean or expected value, which we will explore in more depth with the binomial distribution.

Binomial Random Variable Explained

A binomial random variable represents the number of successes in a series of independent and identically distributed Bernoulli trials, where each trial has only two possible outcomes: success or failure. This kind of random variable is therefore closely tied to the binomial distribution.

If we denote the random variable as ‘X,’ the number of trials as ‘n,’ and the probability of success in an individual trial as ‘p,’ we can predict the probable outcomes of the variable. For example, tossing a coin seven times (n=7) and wanting to know how many times heads will appear (where 'head' is defined as a success) can be modeled by a binomial distribution where the probability of success (p) is 0.5 for each toss.

In this scenario, each toss is independent—the outcome of one toss doesn’t affect the others—and the probability of success remains constant across tosses. These characteristics are pivotal for a scenario to be modeled using a binomial distribution. By identifying the values of ‘n’ and ‘p,’ we can use the binomial distribution to calculate various probabilities and statistical measures, such as the mean.

Statistical Mean of a Binomial Distribution

The statistical mean, also known as the expected value, of a binomial distribution, provides us with an average outcome over a large number of trials. It is calculated by multiplying the number of trials (n) by the probability of success (p), expressed as \(\mu = np\).

This mean tells us what to expect on average; for instance, if we toss a coin seven times, we would expect, on average, to get heads about three and a half times due to the formula \(\mu = 7 \times 0.5 = 3.5\). The mean is an invaluable tool because it gives us a simple summary of the distribution's central tendency. However, it doesn’t tell us everything—other measures like variance and standard deviation also provide insight into the spread of the data around this mean.

To better understand and predict outcomes, especially in cases where the probability of success is not as intuitive as a coin toss, accurately calculating the mean of a binomial distribution is critical. It aids in determining the likeliness of various counts of success across our trials, allowing for deeper insights into the probability of various scenarios.