sequences

[mkhanna]

Data sufficiency question
Q) In the sequence: A(n) = A(n-1) + k; where 2<=n<=15 and k is a non-zero constant, how many terms in the sequence are greater than 10?
1) A(1) = 24
2) A(8) = 10

[tom4lax]

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.

[praky_rules]

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!

[tom4lax]

Right, but question stem states that N must be between 2 and 15.

[praky_rules]

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

[tom4lax]

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?

[crackgmat007]

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.

[mkhanna]

Answer is B. Source = Gmatprep test

Thanks for the explananation!

[gmat550]

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

[kaulnikhil]

B sufficient

[Matmasi]

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