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A made-up survey of 200 adults finds that 120 read the news online, 70 read a paper and 45 do both…

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Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A made-up survey of $200$ adults finds that $120$ read the news online, $70$ read a paper and $45$ do both. One adult from the survey is picked at random. Find the probability that the adult reads the news in at least one of the two ways, the probability of neither, and the probability of online only.

Need a reminder? The key ideaShow

$P(\text{not } A) = 1 - P(A)$ . For any two events $P(A \cup B) = P(A) + P(B) - P(A \cap B)$ . If $A$ and $B$ are mutually exclusive, the overlap is $0$ .

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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