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Expert replies
by ketkoag » Sat Sep 05, 2009 12:14 pm
please explain this one
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Source: — Data Sufficiency |

Re: prep

by qwe12 » Sun Sep 06, 2009 12:31 am
ketkoag wrote:please explain this one
DIFFICULT!

(1) a_2 = a_1 + k; a_1 = 24

Here we have no idea if k is positive or negative, which means we have no idea how many elements are greater than 10. If k was 1, all 15 elements would be greater than 10. If k was -24 we would have only 1 element greater than 10.

NOT SUFFICIENT.

(2) a_8 = 10 = a_7 + k

a_8 is smack in the middle of a_1 through a_15. If k were negative (say -1), then a_9 would 9, which is certainly be less than 10 and a_10 would be 8 and so on, giving us 7 elements greater than 10. The reverse applies if k were positive (say 1), then a_9 would be 11, a_10 would be 11 and so on, giving us 7 elements greater than 10. So irrespective of what the value of k is, we have 7 elements.

SUFFICIENT

(B)
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by ketkoag » Sun Sep 06, 2009 6:39 am
nice explanation, thanks
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