A survey of 200 people in a community who watched at least one of the three channels — BBC, CNN and DD —showedthat 80% of the people watched DD, 22% watched BBC and 15% watched CNN
Question: 1
What is the maximum percentage of people who can watch all the three channels?
Show Hint
When calculating the maximum intersection of multiple sets, the answer is always bounded by the size of the smallest set.
We are told:
$n(DD) = 80%$, $n(BBC) = 22%$, $n(CNN) = 15%$ of 200 people.
The maximum possible number of people who can watch all three channels is limited by the smallest group’s size, which is CNN at 15%.
Hence, the maximum possible percentage = $15%$.
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Question: 2
If 5% of people watched DD and CNN, 10% watched DD and BBC, then what percentage of people watched BBC and CNN only?
Show Hint
In “only” intersection problems, you must subtract the triple intersection from the two-set intersection to get the result.
We know:
$n(DD \cap CNN) = 5%$, $n(DD \cap BBC) = 10%$.
We are asked for $n(BBC \cap CNN \ \text{only}) = n(BBC \cap CNN) - n(BBC \cap CNN \cap DD)$.
Since neither $n(BBC \cap CNN)$ nor the triple intersection is given, we cannot compute this value.
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Question: 3
Referring to the previous question, what percentage of people watched all the three channels?
Show Hint
For triple intersections in Venn diagrams, you must have either direct data or be able to deduce it from given overlaps and totals.
From the given data: $n(DD \cap CNN)$ and $n(DD \cap BBC)$ are known, but there is no information on $n(BBC \cap CNN)$ or $n(DD \cap BBC \cap CNN)$.
Without knowing these, the triple intersection cannot be determined.