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sequence problem

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Senior | Next Rank: 100 Posts
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by anwarma » Thu Jun 12, 2008 5:54 am
What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7, … whose nth term is n+2^n-1?

(A) 2
(B) 3
(C) 6
(D) 16
(E) 17

ANS is E

I want to know, how the answer is 17.
AA
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by litteraround » Thu Jun 12, 2008 7:53 am
hi,
you should post the question more clearly. The nth term is n+[2^(n-1)]. The way you posted it, it could be interpreted in more than one ways.

So, now the sixth term is: 6+2^(6-1) = 6 + 2^(5) = 6+32= 38.

And the fifth term is: 5+2^(5-1) = 5 +2^(4) = 5+16 = 21.

Therefore, the difference is 38-21 = 17. Voila!
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by anwarma » Thu Jun 12, 2008 8:15 am
Thanks!
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