Ellen takes a multiple-choice quiz that has 4 questions, with 3 answer choices for each question. What is the probability that she will get exactly 1 answer correct by guessing? Probabilities should be entered as fractions in simplest form, decimals rounded to the nearest thousandth, or percents rounded to the nearest tenth.

Answer: The probability is  32/81, or  0.395 in decimal form

Step-by-step explanation:

Each question has 3 answers.

one of the answers is correct, and 2 are incorrect.

Then the probability of selecting at random the correct answer, is equal to the quotient between the number of correct answers and the total number of answers, this is:

p = 1/3.

Then the probability of answering wrong is:

q = 1 - 1/3 = 2/3.

Now, we want to find the probability of answering exactly one question correctly.

Let's suppose that Ellen answers correctly the first question, and incorrectly the other 3.

then we have the probability 1/3 one time, and the probability 2/3 3 times.

And as we know, the joint probability will be equal to the product of the individual probabilities, this is:

P = (1/3)*(2/3)*(2/3)*(2/3).

But this is for the case where only the first one is answered correctly, we also have the cases where:

the 2nd is the only one answered correctly

the 3rd is the only one answered correctly

the 4th is the only one answered correctly.

Then we have 4 permutations, which means that the actual probability of answering only on question correctly is:

P' = 4*P = 4*(1/3)*(2/3)*(2/3)*(2/3) = (4*2*2*2)/(3*3*3*3) = 32/81 = 0.395

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