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Senior Manager
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What is the missing term? 1, 7, 17, 31, ? , 71, 97 ... [#permalink]
 05 May 2007, 11:52
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
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Manager
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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.
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Manager
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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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Director
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49..Doesn't looks like GMAT question though...
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Senior Manager
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Hi
The OA is B.
The formula of n-term here is 2*n^2 - 1
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VP
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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.
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close
