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What is the missing term? 1, 7, 17, 31, ? , 71, 97 ...

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Senior Manager
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What is the missing term? 1, 7, 17, 31, ? , 71, 97 ...  [#permalink]

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New post 05 May 2007, 11:52
00:00
A
B
C
D
E

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What is the missing term?
1, 7, 17, 31, ? , 71, 97 ...

A) 45
B) 49
C) 51
D) 53
E) 59
Manager
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New post 05 May 2007, 12:23
I'm stuck between D and E, the the only primes in the list. I'm going with D for an arbitrary reason.

Edit: E) 59. The difference between the numbers increases by 4 each time.
Manager
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Kudos [?]: 7 [0], given: 0

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New post 11 May 2007, 22:30
The answer is B - 49

The difference increases by 4

1,7= 6

7,17= 10

17,31= 14

31,x=18

x,71 = 22

71, 97=26


31+18=49


Hope this helps!! :)
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Kudos [?]: 49 [0], given: 0

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New post 11 May 2007, 23:19
49..Doesn't looks like GMAT question though...
Senior Manager
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New post 12 May 2007, 02:33
Hi

The OA is B.
The formula of n-term here is 2*n^2 - 1
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New post 12 May 2007, 03:43
Juaz wrote:
49..Doesn't looks like GMAT question though...


I agree - doesn't look like a GMAT question.

1,7,17,31,x,71,97

looking for an avarege

(224+x)/7 = integer

since 224/7 = 32

x/7 has to be an integer

so the answer has to be (B) meaning 49

maybe not a GMAT question but nevertheless a good one.

:-D
  [#permalink] 12 May 2007, 03:43
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What is the missing term? 1, 7, 17, 31, ? , 71, 97 ...

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