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Re: On a certain table is a collection of 45 pens of various col [#permalink]
4
Here is another approach.
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Re: On a certain table is a collection of 45 pens of various col [#permalink]
1
To my mind, this would be the reasoning here; feel free to correct me if I'm wrong:
1. We know the total number of pens (45).
2. We know that exactly 27 pens are ballpoint and that 27 pens contain blue ink.
3. We know that they have to overlap for two reasons: (1) on an obvious/intuitive level, 60% is more than half, so it's impossible for the two not to overlap in that 45-pen system, and (2), we can see that if we add up 27 and 27, we get 54, which is more than the total number of pens on the table.

4. Since we know they have overlap, we could define that this way:
Total = Set1 + Set2 - Overlap
45 = 27 + 27 - O
45 = 54 - O
O = 9

5. Since 9 > 8, the answer is A.
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On a certain table is a collection of 45 pens of various col [#permalink]
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We want to know what is the min and max of the intersection of Ball Point and Blue.

The max is the case where all Ball Point pens are also blue, i.e. intersection would be 27

*Visualizing a two group Venn Diagram*
The underlying idea to get the min is: WE MINIMIZE THE INTERSECTION WHEN WE LET THE THE GROUP OUTSIDE THE UNION BE AT ITS SMALLEST.

Why? By making the group outside the union as small as possible, we "free up space" for the union to be as large as possible. Why is this important? Because with more free space we are allowed to "separate" the groups of Ball Point Pens and Blue pens further apart, hence making the intersection smaller.

Let x=QA.
We let the groups outside the union be 0.
Therefore
45=27+27-x
x=9

Therefore QA is between 9 and 27 inclusive

Final Answer: A
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Re: On a certain table is a collection of 45 pens of various col [#permalink]
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