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

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Senior Manager
Joined: 04 Mar 2007
Posts: 442
Followers: 1

Kudos [?]: 17 [0], given: 0

What is the missing term? 1, 7, 17, 31, ? , 71, 97 ...  [#permalink]  05 May 2007, 10:52
00:00

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(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
What is the missing term?
1, 7, 17, 31, ? , 71, 97 ...

A) 45
B) 49
C) 51
D) 53
E) 59
Manager
Joined: 23 Dec 2006
Posts: 136
Followers: 1

Kudos [?]: 11 [0], given: 0

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
Joined: 09 Sep 2004
Posts: 166
Followers: 1

Kudos [?]: 1 [0], given: 0

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!!
Director
Joined: 18 Jul 2006
Posts: 531
Followers: 1

Kudos [?]: 30 [0], given: 0

49..Doesn't looks like GMAT question though...
Senior Manager
Joined: 04 Mar 2007
Posts: 442
Followers: 1

Kudos [?]: 17 [0], given: 0

Hi

The OA is B.
The formula of n-term here is 2*n^2 - 1
VP
Joined: 08 Jun 2005
Posts: 1147
Followers: 6

Kudos [?]: 128 [0], given: 0

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

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.

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