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test 13 #12

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test 13 #12

by dunkin77 » Mon Apr 23, 2007 2:23 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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by mschling52 » Thu Apr 26, 2007 9:47 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.
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by f2001290 » Thu Apr 26, 2007 8:47 pm
I agree with both of you . It should be D.
Last edited by f2001290 on Wed May 16, 2007 9:53 pm, edited 1 time in total.
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by arielsky » Sun Apr 29, 2007 4:30 am
sorry...can someone explain why it wouldnt be C? how do we know where to start off if we arent given the first term?
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by arielsky » Sun Apr 29, 2007 4:32 am
oh wait sorry, i got confused, choice c always states that both of them together are useful but each alone is not, which isnt the case here.
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