in the first choice, we are given the first term. we dont have any value for k.
so insuff... we cant tell if k is positive or negative. eliminate a,d
from 2.) if u carefully check its the middle term of the 15 terms. the no of terms is odd. so, in any case there are seven terms below a8 and seven terms above a8. so it is suff to answer the question. hence B.

hope it helps..

moneyman wrote:I dont understand how B is sufficient

jimmiejaz - great work.

Moneyman,


You can see that:

a2 = a1 + k
a3= a2 +k or, (a1+k) + k

which is a1+2k

in other words this is how your series look like

a1, a1+k, a1+2k, ......, a1+14k

and remember we have 15 terms in this series

a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 a14 a15

and a8 is in the middle

but the question or the answers have no information about what k is

but if we know that a8 = 10, either k is negative or positive, we will have 7 numbers greater than 10.


a1 a2 a3 a4 a5 a6 a7

or

a9 a10 a11 a12 a13 a14 a15

Thanks jimmiejaz..It looks like an evenly spaced set then isnt the middle number the average as well?

moneyman wrote:Thanks jimmiejaz..It looks like an evenly spaced set then isnt the middle number the average as well?

yes ... you got it right mate!!!!
in an evenly spaced set or a set of consecutive integers, the mean is the median.

Hope it helps.