Compare Quantity A and Quantity B, using additional information centered above the two quantities if such information is given,

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问题 Compare Quantity A and Quantity B, using additional information centered above the two quantities if such information is given, and select one of the following four answer choices:
(A)Quantity A is greater.
(B)Quantity B is greater.
(C)The two quantities are equal.
(D)The relationship cannot be determined from the information given.
A symbol that appears more than once in a question has the same meaning throughout the question.
n is a positive integer that is greater than 3 and has d positive divisors.

选项

答案D

解析 Since there is no obvious relationship between the quantities n and 2d-1, it is a good idea to try a few values of n to see what happens. Note that you are given that n is an integer greater than 3, so you can start comparing the quantities for the case n = 4 and proceed from there.
Case 1: n = 4. The integer 4 has three positive divisors, 1, 2, and 4. So in this case, d = 3. Therefore 2d-1= 23-1= 4, and the two quantities are equal.
Case 2: n= 5. The integer 5 has two positive divisors, 1 and 5. So in this case, d = 2. Therefore 2d-1= 22-1= 2, and Quantity A is greater than Quantity B.
In one case the two quantities are equal, and in the other case Quantity A is greater than Quantity B. Therefore the correct answer is Choice D.
This explanation uses the following strategies.
Strategy 10: Trial and Error
Strategy 13: Determine Whether a Conclusion Follows from the Information Given
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本试题收录于: GRE QUANTITATIVE题库GRE分类
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