Data Sufficiency

Interesting question. I'll post the OA after few folks reply.

Is it B?

(1) Just knowing a1 doesn't help as k is unknown. If k is a big negative number, all terms might be less than 10, and if k is huge positive number, all may be greater than 10.

(2) If k is positive, a9 through a15 (7 terms) are greater than 10 and a1 through a7 (7 terms) are less than 10.
If k is negative, a9 through a15 are less than 10 and a1 through a7 are more than 10.
So in either case the answer is 7.

rajesh_ctm wrote:Is it B?

(1) Just knowing a1 doesn't help as k is unknown. If k is a big negative number, all terms might be less than 10, and if k is huge positive number, all may be greater than 10.

(2) If k is positive, a9 through a15 (7 terms) are greater than 10 and a1 through a7 (7 terms) are less than 10.
If k is negative, a9 through a15 are less than 10 and a1 through a7 are more than 10.
So in either case the answer is 7.

good analysis ...

me too getting the answer as B .. reason same as above ...

Good one, guys.

OA is indeed B.