Beat The GMAT

dunkin77 · Mon Apr 23, 2007 3:23 pm

12. In a sequence of numbers in which each term after the first term is 1 more than twice the preceding term, what is the fifth term?

(1) The first term is 1.
(2) The sixth term minus the fifth term is 32.

Hi,

I thoght the question is x, 2x+1, 2(2x+1)+1, ..... and chose D), but the correct answer is B) -- Can anyone please explain??

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mschling52 · Thu Apr 26, 2007 10:47 am

I agree with you on D...Seems like (1) allows you to construct the sequence, since a1 = 1 we have

1, 3, 7, 15, 31, ..... and a5 = 31

(2) gives us

a6 - a5 = 32
2a5 + 1 - a5 = 32
a5 = 31

So, I agree that each alone is sufficient, but maybe I am missing something as to why (1) isn't.