Calculate probability of either of two events occurring based on frequency

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Question 1

Out of $\var{ptotal}$ people, $\var{p1}$ play Go, $\var{p2}$ play Chess, $\var{p3}$ play both, and $\var{p4}$ play neither.

Calculate the probability that a person selected at random plays Go. Write your answer as a fraction.

$\displaystyle{}$ Expected answer:

$\displaystyle{\frac{ 20 }{ 41 }}$

Score: 0/1.5

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Calculate the probability that a randomly selected person plays Chess or Go. Give your answer as a fraction.

$\displaystyle{}$ Expected answer:

$\displaystyle{\frac{ 83 }{ 123 }}$

Score: 0/3

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Calculate the probability that a randomly selected person plays Chess but not Go.

$\displaystyle{}$ Expected answer:

$\displaystyle{\frac{ 23 }{ 123 }}$

Score: 0/4.5

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