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Use the following information to answer the next two exercises: The probability that the San Jose Sharks will win any given game is 0.3694 based on a 13-year win history of 382 wins out of 1,034 games played (as of a certain date). An upcoming monthly schedule contains 12 games. A student takes a ten-question true-false quiz, but did not study and randomly guesses each answer. Find the probability that the student passes the quiz with a grade of at least 70% of the questions correct.

Short Answer

Expert verified
The probability is approximately 0.1719 or 17.19%.

Step by step solution

01

Define the problem

We have a 10-question true-false quiz, and the student randomly guesses each answer. The probability of guessing any single answer correctly is 0.5. We need to find the probability that the student answers at least 7 out of the 10 questions correctly.
02

Use the Binomial Probability Formula

The situation is a binomial probability problem where each question is an independent trial, with two outcomes: correct or incorrect. Use the formula for binomial probability: \[ P(X = k) = \binom{n}{k} p^k (1-p)^{n-k} \]where \( n = 10 \) (number of trials), \( p = 0.5 \) (probability of success), \( k \) is the number of successes.
03

Calculate Probability for Exact Successes

Calculate the probability for each k where k is 7, 8, 9, and 10 since the student needs to answer at least 7 questions correctly.\[ P(X = 7) = \binom{10}{7} (0.5)^7 (0.5)^{3} \]\[ P(X = 8) = \binom{10}{8} (0.5)^8 (0.5)^{2} \]\[ P(X = 9) = \binom{10}{9} (0.5)^9 (0.5)^{1} \]\[ P(X = 10) = \binom{10}{10} (0.5)^{10} (0.5)^{0} \]
04

Calculate Individual Probabilities

Calculate each probability:- \( P(X = 7) = \binom{10}{7} (0.5)^{10} = 120 \times 0.5^{10} \)- \( P(X = 8) = \binom{10}{8} (0.5)^{10} = 45 \times 0.5^{10} \)- \( P(X = 9) = \binom{10}{9} (0.5)^{10} = 10 \times 0.5^{10} \)- \( P(X = 10) = \binom{10}{10} (0.5)^{10} = 1 \times 0.5^{10} \)
05

Sum Probabilities

Sum the probabilities of getting at least 7 correct answers:\[ P(X \geq 7) = P(X = 7) + P(X = 8) + P(X = 9) + P(X = 10) \]\[ P(X \geq 7) = 120 \times 0.5^{10} + 45 \times 0.5^{10} + 10 \times 0.5^{10} + 1 \times 0.5^{10} \]\[ P(X \geq 7) = (120 + 45 + 10 + 1) \times 0.5^{10} \]\[ P(X \geq 7) = 176 \times 0.5^{10} \]Calculate \( 0.5^{10} = 0.0009765625 \), then \[ P(X \geq 7) = 176 \times 0.0009765625 = 0.171875 \]
06

Conclusion

The probability that a student passes the quiz by answering at least 7 questions correctly is \( 0.171875 \), or approximately 17.19%.

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Key Concepts

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

Probability of Success
In the context of probability, the term "Probability of Success" refers to the likelihood of a specific outcome happening in a single trial of an experiment. For example, when a student randomly guesses answers in a true-false quiz, the probability of guessing correctly is 0.5. This is because there are only two possible outcomes for each question: true or false, and each has an equal chance of being right.

The probability of success is a fundamental concept in binomial experiments, where you perform a fixed number of trials, each trial having two possible outcomes. It's often represented by the symbol \( p \). In cases like a true-false quiz, \( p = 0.5 \) as each answer (true or false) is equally probable. Understanding the probability of success helps in calculating how likely it is to achieve a certain number of successful outcomes over multiple trials.

For example, if the student needs to get 7 out of 10 questions right to pass, their probability of success remains the same for each question, 0.5, but you analyze the cumulative probability over several trials to determine the overall chance of passing.
Binomial Distribution
The concept of a "Binomial Distribution" is crucial when dealing with experiments that involve repeated and independent trials, like a true-false quiz. In a binomial distribution, there are a set number of trials (\( n \)), and each trial can result in just two outcomes: success or failure. This kind of setup is called a "binomial experiment."

To calculate probabilities within a binomial distribution, we use the binomial probability formula:\[P(X = k) = \binom{n}{k} p^k (1-p)^{n-k} \]Where:- \( n \) is the total number of trials (e.g., 10 questions on a quiz).- \( p \) is the probability of success for each trial (e.g., 0.5 for guessing a true or false answer).- \( k \) is the number of successful trials we are interested in.- \( \binom{n}{k} \) is a combination function, representing how many ways \( k \) successes can occur in \( n \) trials.

In our true-false quiz scenario, we use the binomial distribution to find the likelihood that our student passes the quiz. By adding the probabilities \( P(X = 7), P(X = 8), P(X = 9), \) and \( P(X = 10) \), we find the overall probability that the student achieves the required number of correct answers to pass.
True-False Quiz
True-False quizzes are a common example in probability exercises due to their simplicity. These quizzes consist of questions with only two possible answers: true or false. This dichotomy makes them perfect for understanding binomial experiments because each question acts as a separate trial with two possible outcomes.

In a true-false quiz, if a student guesses the answers without any knowledge about the questions, each question has a 50% chance of being answered correctly. This probability forms the basis for determining larger outcome probabilities using binomial distribution.

Analyzing a true-false quiz through probability provides a practical application for understanding binomial probability distributions in the real world. Whether it's for academic exercises or evaluating how random guessing affects outcomes, true-false quizzes can be a fun way to explore fundamental mathematical concepts.

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Most popular questions from this chapter

Use the following information to answer the next seven exercises: A ballet instructor is interested in knowing what percent of each year's class will continue on to the next, so that she can plan what classes to offer. Over the years, she has established the following probability distribution. \(\bullet\) Let \(X=\) the number of years a student will study ballet with the teacher. \(\bullet\) Let \(P(x)=\) the probability that a student will study ballet \(x\) years. In words, define the random variable \(X\).

Identify the mistake in the probability distribution table. $$\begin{array}{|c|c|c|}\hline x & {P(x)} & {x^{*} P(x)} \\ \hline 1 & {0.15} & {0.15} \\ \hline 2 & {0.25} & {0.40} \\ \hline 3 & {0.25} & {0.85} \\\ \hline 4 & {0.20} & {0.85} \\ \hline 5 & {0.15} & {1} \\ \hline\end{array}$$

Use the following information to answer the next four exercises. Recently, a nurse commented that when a patient calls the medical advice line claiming to have the flu, the chance that he or she truly has the flu (and not just a nasty cold) is only about 4%. Of the next 25 patients calling in claiming to have the flu, we are interested in how many actually have the flu. State the distribution of \(X.\)

Use the following information to answer the next two exercises: The average number of times per eek that Mrs. Plum’s cats wake her up at night because they want to play is ten. We are interested in the number of times her cats wake her up each week. In words, the random variable \(X =\) _________________ a. the number of times Mrs. Plum’s cats wake her up each week. b. the number of times Mrs. Plum’s cats wake her up each hour. c. the number of times Mrs. Plum’s cats wake her up each night. d. the number of times Mrs. Plum’s cats wake her up.

A venture capitalist, willing to invest \(\$ 1,000,000\), has three investments to choose from. The first investment, a software company, has a 10% chance of returning \(\$ 5,000,000\) profit, a 30% chance of returning \(\$ 1,000,000\) profit, and a 60% chance of losing the million dollars. The second company, a hardware company, has a 20% chance of returning \(\$ 3,000,000\) profit, a 40% chance of returning \(\$ 1,000,000\) profit, and a 40% chance of losing the million dollars. The third company, a biotech firm, has a 10% chance of returning \(\$ 6,000,000\) profit, a 70% of no profit or loss, and a 20% chance of losing the million dollars. a. Construct a PDF for each investment. b. Find the expected value for each investment. c. Which is the safest investment? Why do you think so? d. Which is the riskiest investment? Why do you think so? e. Which investment has the highest expected return, on average?

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