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Review: Students Who Got Both Questions Correct
Explanation
This is an overlapping sets question of two sets, so we
can draw a Venn diagram or cut straight to the formula 
.
Filling in what we know, we get
We care about B,
so we can isolate it:
The question tells us that N must be at least 10, so B must
be at least 80. That narrows the answer choices to (D) and (E). From an
arithmetic standpoint, B could range
freely; the upper constraint is logically derived. It boils down to the fact
that if 100 got the first question correct, then the number that got both
questions correct cannot be greater than 100.
The correct answer is (D).
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