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The student calculates the probability that he will get all the questions correct by guessing.

\begin{tabular}{|c|c|c|}
\hline
& To get 100\% correct: & [tex][tex]$P$[/tex][/tex] (guess is correct) \\
\hline
History & \begin{tabular}{c}
Answer 5 of 5 \\
correctly.
\end{tabular} & 0.5 \\
\hline
Science & \begin{tabular}{c}
Answer 3 of 3 \\
correctly.
\end{tabular} & 0.25 \\
\hline
\end{tabular}

The student will study for the quiz on which he is likely to do worse by guessing. Which quiz should he study for?

A. History, because he must get more questions correct.
B. Science, because the probability of getting all questions correct is 0.016, which is lower than for history (0.031).
C. History, because the probability of getting all questions correct is 0.031, which is lower than for science (0.75).
D. Science, because the probability of getting all questions correct is 0.075, which is lower than for history [tex][tex]$(0.25)$[/tex][/tex].


Sagot :

To determine which quiz the student should study for by comparing the probabilities of getting all questions correct, let's first find the probabilities for both subjects.

### History Quiz
\- Number of questions: [tex]\( 5 \)[/tex]
\- Probability of getting each question correct: [tex]\( 0.5 \)[/tex]

To find the probability of getting all [tex]\( 5 \)[/tex] questions correct in history, we need to raise the individual probability to the power of the number of questions:
[tex]\[ P(\text{all correct in history}) = 0.5^5 = \frac{1}{2^5} = \frac{1}{32} = 0.03125 \][/tex]

### Science Quiz
\- Number of questions: [tex]\( 3 \)[/tex]
\- Probability of getting each question correct: [tex]\( 0.25 \)[/tex]

To find the probability of getting all [tex]\( 3 \)[/tex] questions correct in science, we raise the individual probability to the power of the number of questions:
[tex]\[ P(\text{all correct in science}) = 0.25^3 = \left(\frac{1}{4}\right)^3 = \frac{1}{4^3} = \frac{1}{64} = 0.015625 \][/tex]

Now, we compare the probabilities:
\- Probability of getting all questions correct in history: [tex]\( 0.03125 \)[/tex]
\- Probability of getting all questions correct in science: [tex]\( 0.015625 \)[/tex]

Since the probability of getting all questions correct in science ([tex]\( 0.015625 \)[/tex]) is lower than the probability of getting all questions correct in history ([tex]\( 0.03125 \)[/tex]), the student is less likely to guess all questions correctly in the science quiz.

Therefore, the student should study for the quiz where the chances of guessing all questions correctly are lower, which is the science quiz.

Thus, the correct answer is:
[tex]\[ \text{B. Science, because the probability of getting all questions correct is 0.016, which is lower than for history (0.031).} \][/tex]