Bunuel wrote:
If all members of Set X are positive integers, what is the range of Set X?
(1) The positive difference between the square of the largest number in Set X and the square of the smallest number in Set X is 99.
(2) The sum of the largest number in Set X and the smallest number in Set X is 11.
Target question: What is the range of Set X?This is a good candidate for
rephrasing the target question.
Let G = the Greatest number in set X
Let L = the Least number in set X
REPHRASED target question: What is the value of G - L? Statement 1: The positive difference between the square of the largest number in Set X and the square of the smallest number in Set X is 99. In other words, G² - L² = 99
Factor left side: (G + L)(G - L) = 99
IMPORTANT: Using only positive integers, there are only 3 different ways to get a product of 99:
(99)(1) = 99
(33)(3) = 99
(11)(9) = 99
Since G and L are positive INTEGERS, we know that (G + L) is an integer, and (G - L) is an integer
So, only 3 scenarios are possible:
Scenario #1: (G + L) = 99, and (G - L) = 1
Scenario #2: (G + L) = 33, and (G - L) = 3
Scenario #3: (G + L) = 11, and (G - L) = 9 For Scenario #1, the answer to the REPHRASED target question is
G - L = 1For Scenario #2, the answer to the REPHRASED target question is
G - L = 3For Scenario #3, the answer to the REPHRASED target question is
G - L = 9Since we cannot answer the
REPHRASED target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: The sum of the largest number in Set X and the smallest number in Set X is 11There are several values of G and L that satisfy statement 2. Here are two:
Case a: G = 8 and L = 3. In this case, the answer to the REPHRASED target question is
G - L = 5Case b: G = 10 and L = 1. In this case, the answer to the REPHRASED target question is
G - L = 9Since we cannot answer the
REPHRASED target question with certainty, statement 2 is NOT SUFFICIENT
Statements 1 and 2 combined Statement 1 yielded exactly 3 scenarios:
Scenario #1: (G + L) = 99, and (G - L) = 1
Scenario #2: (G + L) = 33, and (G - L) = 3
Scenario #3: (G + L) = 11, and (G - L) = 9 Statement 2 tells us that G + L = 11
When we examine the possible scenarios, only one (scenario #3) satisfies the condition that G + L = 11
Scenario #3 also tell us that
(G - L) = 9Since we can answer the
REPHRASED target question with certainty, the combined statements are SUFFICIENT
Answer: C
Cheers,
Brent
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Brent Hanneson – Creator of gmatprepnow.com
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