Of the 100 people, 72% bought stocks and 65% bought bonds. What is the number of people who bought stocks but not bonds?
1) The number of people who bought both stocks and bonds is 45
2) The number of people who bought neither stocks nor bonds is 8
==> If you modify the original condition and the question, you get a 2 by 2, as shown on the table below.
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From a+b+c+d=100, a+c=100(72%)=72, and a+b=100(65%)=65, there are 4 variables and 3 equations. In order to match the number of variables to the number of equations, there must be 1 more equation. Since there is 1 for con 1) and 1 for con 2), D is most likely to be the answer.
For con 1), from a=45, you get 45+c=27, hence c=27 and it is unique and sufficient.
For con 2), from d=8, you get a+b+c+d=65+c+8=100, hence c=27 and it is unique and sufficient.
Therefore, the answer is D.
Answer: D
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