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Let \(x\) be a binomial random variable for \(n=30\) and \(p=0.1.\) a. Explain why the normal approximation is not reasonable. b. Find the function used to calculate the probability of any \(x\) from \(x=0\) to \(x=30\) c. Use a computer or calculator to list the probability distribution.

Short Answer

Expert verified
a) The normal approximation is not reasonable as the np is less than 5. b) The function used is the binomial function: \(P(x) = C(n, x) * p^x * (1-p)^{n-x}\). c) The probability distribution would be computed using a calculator or a computer program for every \(x\) ranging from 0 to 30.

Step by step solution

01

Understanding the normal approximation

For a binomial distribution, the normal approximation is generally considered to be a reasonable estimation when both \(np\) and \(n(1-p)\) are greater than 5. Here, \(np = 30 * 0.1 = 3\) and \(n(1-p) = 30 * 0.9 = 27.\) Since np is not greater than 5, it suggests that the normal approximation might not be accurate in this case.
02

Calculating the binomial probability function

The binomial function is used to calculate the probability of any \(x\). It's defined as: \[ P(x) = C(n, x) * p^x * (1-p)^{n-x} \] where \(C(n, x)\) is the number of combinations of \(n\) items taken \(x\) at a time, \(p\) is the probability of success, and \(n\) is the number of trials. So, we'll use this function to calculate the probability of \(x\) from \(x=0\) to \(x=30\).
03

Listing the probability distribution

For this step, we use the binomial function defined in step 2 and calculate the probabilities for each possible value of \(x\) from 0 to 30. This can be done using a scientific calculator or a statistical software.
04

Answering the questions

a) The normal approximation is not reasonable because \(np < 5.\) b) The function used to calculate the probability is the binomial function: \[ P(x) = C(n, x) * p^x * (1-p)^{n-x} \] c) The probability distribution was generated using a computer or calculator by inputting the values of \(n=30\) and \(p=0.1\) into the binomial function and calculating it for each \(x\) from 0 to 30.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Normal Approximation
When dealing with a binomial distribution, the normal approximation can be a very handy tool. However, it is crucial to understand when it is applicable. To determine whether we can use this approximation, we look at the product of the number of trials () and the probability of success (p), as well as times the probability of failure ((1-p)). The rule of thumb is that if both p and (1-p) are greater than 5, then the normal approximation is suitable.

In our exercise, with =30 and p=0.1, we calculate p as 30 * 0.1 = 3 and (1-p) as 30 * 0.9 = 27. Since the p value is less than 5, the conditions for normal approximation aren't met. In layman's terms, this means our distribution is skewed too much, lacking the symmetric 'bell curve' shaped like a normal distribution needed for a reasonable approximation. Thus, describing our binomial distribution with a normal one would likely lead to inaccurate results, particularly for probabilities of events that fall on the lower end of the spectrum.
Binomial Probability Function
The binomial probability function is the linchpin for calculating the likelihood of different outcomes for a binomial distribution. In simpler terms, it tells us the probability of getting a certain number of successes in a fixed amount of trials, given the probability of success on each trial. The formula looks like this: \[ P(x) = C(n, x) * p^x * (1-p)^{n-x} \] where denotes the number of trials, p stands for the probability of a single success, and C(n, x) represents the number of combinations of items taken x at a time. For instance, if you were flipping a coin 30 times and wanted to know the probability of getting exactly 10 heads, the binomial probability function would give you the precise odds.

To better understand, let's break down the parts of the formula: C(n, x) calculates the different ways x successes can occur within n trials, p^x represents the probability of achieving x successes, and (1-p)^{n-x} accounts for the probability of the remaining trials resulting in failure. Each of these parts works together to provide a comprehensive picture of the binomial probability for any given number of successes.
Probability Distribution
A probability distribution, in a broad sense, is just a table or an equation that links each outcome of a statistical experiment with its probability of occurrence. For a binomially distributed random variable, this distribution illustrates the probability of achieving a range of successes in a fixed number of trials given a specific probability of success in each trial.

In the context of the exercise, listing the probability distribution involves using the binomial probability function to calculate the probability for each possible outcome (from 0 to 30 successes). It's important to outline that, these values tell a story - they convey not just the chances of one particular outcome but also let you see how likely different numbers of successes are compared to others.

To visualize this, think of plotting the calculated probabilities on a graph. As the number of successes increases, does the likelihood rise or fall? Is there a certain number of successes that is most probable, or does it spread out evenly? Plotting the probability distribution based on the calculated values provides these insights, which can be immensely valuable for probabilistic intuition and understanding the underlying binomial process at play.

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Most popular questions from this chapter

We are often interested in finding the value of \(z\) that bounds a given area in the right-hand tail of the normal distribution, as shown in the accompanying figure. The notation \(z(\alpha)\) represents the value of \(z\) such that \(P(z>z(\alpha))=\alpha.\) Find the following: a. \(\quad z(0.025)\) b. \(\quad z(0.05)\) c. \(\quad z(0.01)\)

We are often interested in finding the value of \(z\) that bounds a given area in the left-hand tail of the normal distribution, as shown in the accompanying figure. The notation \(z(\alpha)\) represents the value of \(z\) such that \(P(z>z(\alpha))=\alpha.\) Find the following: a. \(\quad Z(0.98)\) b. \(\quad z(0.80)\) c. \(\quad z(0.70)\)

A company that manufactures rivets used by commercial aircraft manufacturers knows that the shearing strength of (force required to break) its rivets is of major concern. They believe the shearing strength of their rivets is normally distributed, with a mean of 925 pounds and a standard deviation of 18 pounds. a. If they are correct, what percentage of their rivets has a shearing strength greater than 900 pounds? b. What is the upper bound for the shearing strength of the weakest \(1 \%\) of the rivets? c. If one rivet is randomly selected from all of the rivets, what is the probability that it will require a force of at least 920 pounds to break it? d. Using the probability found in part c, what is the probability, rounded to the nearest tenth, that 3 rivets in a random sample of 10 will break at a force less than 920 pounds?

Use a computer or calculator to find the probability that one randomly selected value of \(x\) from a normal distribution, with mean 584.2 and standard deviation 37.3 will have a value a. less than 525. b. between 525 and 590. c. of at least 590. d. Verify the result using Table 3. e. Explain any differences you may find.

In which of the following binomial distributions does the normal distribution provide a reasonable approximation? Use computer commands to generate a graph of the distribution and compare the results to the "rule of thumb." State your conclusions. a. \(\quad n=10, p=0.3\) b. \(\quad n=100, p=0.005\) c. \(\quad n=500, p=0.1\) d. \(\quad n=50, p=0.2\)

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