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I could not help it.
After I have posted my previous reply I have checked in my Kaplan 2003 book.
The correct answer given is E.
Kaplan:
From the question stem: All we know is that x is a prime number. We want enough information to determine which prime number x is. Our method, then, is to try to find more than one prime that fits with whatever information we're given. If we can, the information is insufficient; if we can't - if we can find only one prime that fits with the information - then the information is sufficient.
1) Insufficient: if x < 15, x could be 2, 3, 5, 7, 11 or 13. Eliminate A and D.
2) Insufficient: if (x-2) is a multiple of five, then x is 2 more than a multiple of 5. So the question is: Can we find more than one prime number that is 2 more than a multiple of five? Yes. Multiples of 5 are 0, 5, 10, 15, 20, and so on. Two more than 5 is 7 - a prime number. While 2 more than 10 is 12, which isn't a prime number, 2 more than 15 is 17, which is prime. Eliminate B.
In combination: Statement 1 narrowed down the possible values of x to 2, 3, 5, 7, 11 and 13. Remember that 0 is a multiple of 5 as well. So both 2 and 7 are more than a multiple of 5, so we cannot find a single answer to the question using both statements. Choose E.
Amit_drummer, I am not sure which Kaplan Book you use. This is the info from the 2003 book.
Good one. I have seen these too (actually I missed out 2 and chose C, when I first solved this problem).
When we think of multiples of 5, all we think of is 5, 10, 15, ...
It can be ..., -15, -10, -5, 0, 5, 10, 15, ...
(though negative is not relavent to this problem)
0 is not a multiple of 5 or for that matter any integer.
in that case the LCM of any 2 numbers, will be a 0.
Multiples mean more than ZERO. 1x, 2x, 3x,....etc.
Zero is considered to be a multiple. I believe the LCM is defined to be a positive number. If not, the LCM would be negative infinity since there are an unlimited number of negative numbers that are multiples of two numbers. _________________
Best,
AkamaiBrah Former Senior Instructor, Manhattan GMAT and VeritasPrep Vice President, Midtown NYC Investment Bank, Structured Finance IT MFE, Haas School of Business, UC Berkeley, Class of 2005 MBA, Anderson School of Management, UCLA, Class of 1993
0 is not a multiple of 5 or for that matter any integer.
in that case the LCM of any 2 numbers, will be a 0.
Multiples mean more than ZERO. 1x, 2x, 3x,....etc.
Zero is considered to be a multiple. I believe the LCM is defined to be a positive number. If not, the LCM would be negative infinity since there are an unlimited number of negative numbers that are multiples of two numbers.