In a class of 100 students, 73 like coffee, 80 like tea and 52 like lemonade. It may be possible that some students do not like any of these three drinks. Then the difference between the maximum and minimum possible number of students who like all the three drinks is
A
Step-by-Step Solution
This is a "three-set max-min of the triple intersection" question. The signal is three overlapping groups (coffee, tea, lemonade), a total population, an explicit note that some people may like none of the three, and a question asking for the range (difference between max and min) of the all-three overlap.
Step 1: Set up notation.
Let (total students). Let = coffee likers (), = tea likers (), = lemonade likers (). We want the range of .
Step 2: Find the maximum of the triple intersection.
The triple intersection can never exceed the smallest individual set, because everyone in must also be in the smallest group:
This maximum of 52 is achievable: let all 52 lemonade-likers also like both coffee and tea. This uses only of the students for the triple overlap, and the remaining coffee-only and tea-only requirements ( people needing extra coffee, people needing extra tea) can easily overlap with each other without exceeding the 100-student population (only students needed in total). So the maximum is .
Step 3: Find the minimum of the triple intersection.
To minimize the overlap, we want to spread out the three groups as much as possible, using the full population of 100 to "absorb" as much of each group as possible without needing all three to overlap.
For two sets, the minimum possible overlap is:
This comes from: even if and are spread out as much as possible without overlapping, together they cannot exceed the total population ; any excess beyond must overlap.
Extending this idea to three sets, we get a similar bound by combining with :
Substituting values:
Since 5 is non-negative, this is a valid lower bound, and it is achievable by careful construction (spreading coffee, tea, and lemonade likers to overlap only the minimum necessary amount). So the minimum is .
Step 4: Compute the difference.
So the answer is .
Common trap: a common mistake is computing the minimum using only the two-set formula () and forgetting to extend it properly to three sets, or forgetting the "some students like none" condition entirely and assuming the union must equal exactly 100 rather than being at most 100.