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Source: — Problem Solving |
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by tom4lax » Sun Aug 30, 2009 8:43 am
I A(1) = 24. Doesnt really tell us anything. Insuff.

II A(8) = 10.

Also, A(8) = 24 + 7k so k = -2.

IMO answer is C.
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by praky_rules » Sun Aug 30, 2009 8:50 am
B is sufficient. K can be positive or negative.
If K is positive the terms, A9 to A15 will be greater than 10 (7 terms) and if K is negative, A1 to A7 will be greater than 10(7 terms) - Sufficient!
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by tom4lax » Sun Aug 30, 2009 8:58 am
Right, but question stem states that N must be between 2 and 15.
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by praky_rules » Sun Aug 30, 2009 9:00 am
2 to 15 defines n. not An. A1 is a valid member of the sequence.Otherwise there is no "fun" in the question..I think
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by tom4lax » Sun Aug 30, 2009 9:06 am
I agree, under my assumption, the question is easy and rather boring.

I am probably just misinterpreting the wording of the question, but to me "In the sequence: A(n) = A(n-1) + k; where 2<=n<=15" A(1) is not possible because n must be between 2 & 15. I do realize that (I) gives us info for A(1)... so I am probably wrong.

What is the OA and source?
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by crackgmat007 » Sun Aug 30, 2009 12:48 pm
IMO B.

B gives the value of A8 which is 10. Irrespective of whether k is negative or positive, we know that there are how many terms will be greater than 10.
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by mkhanna » Mon Aug 31, 2009 8:28 am
Answer is B. Source = Gmatprep test

Thanks for the explananation!
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by gmat550 » Tue Sep 01, 2009 9:48 am
since 2<=n<=15 .. A(1) is not accepted because it doesn't follow the condition .. We cannot solve for k..

A(8) = 10, but we have no information about k ..


ANS:
E
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by kaulnikhil » Tue Sep 01, 2009 12:34 pm
B sufficient
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by Matmasi » Wed Sep 02, 2009 12:58 pm
Hi,

I guess that the trick is in understanding that A(1) is part of the sequence.
This is true because, as stated, n can be n=2.
So, from the statement we know that for A(2)= A(2-1) but A(2-1)=A(1)!
so we know that A(1) is still following the rules of the sequence. But, of course we know that A(1) is not equal to A(0).
Given that we see that A(8) is exactly in the middle of the sequence, it has 7 terms on the right and seven terms on the left, so we know that 7 is the number of the terms >10

B

Good study
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