# Probability problem- A student has to sit a multiple-choice test with five questions

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A student has to sit a multiple-choice test with fi ve questions. Each question has five answer choices.

Only one of the choices is correct. He does not know what the answer is to any question, so he

guesses the answer randomly. Find the probability of answering

a) the fi rst question correctly;

b) the first two questions correctly;

c) exactly two questions correctly;

d) none of the questions correctly;

e) at least one of the questions correctly.

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##### Solution Summary

This solution provides steps to determine the answers to each of the probability problems.

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Question. A student has to sit a multiple-choice test with five questions. Each question has five answer choices. Only one of the choices is correct. He does not know what the answer is to any question, so he guesses the answer randomly. Find the probability ...

###### Education

- BSc , Wuhan Univ. China
- MA, Shandong Univ.

###### Recent Feedback

- "Your solution, looks excellent. I recognize things from previous chapters. I have seen the standard deviation formula you used to get 5.154. I do understand the Central Limit Theorem needs the sample size (n) to be greater than 30, we have 100. I do understand the sample mean(s) of the population will follow a normal distribution, and that CLT states the sample mean of population is the population (mean), we have 143.74. But when and WHY do we use the standard deviation formula where you got 5.154. WHEN & Why use standard deviation of the sample mean. I don't understand, why don't we simply use the "100" I understand that standard deviation is the square root of variance. I do understand that the variance is the square of the differences of each sample data value minus the mean. But somehow, why not use 100, why use standard deviation of sample mean? Please help explain."
- "excellent work"
- "Thank you so much for all of your help!!! I will be posting another assignment. Please let me know (once posted), if the credits I'm offering is enough or you ! Thanks again!"
- "Thank you"
- "Thank you very much for your valuable time and assistance!"

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