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Direction: In each of these questions a number series is given. Only one number is wrong in each series. You have to find out the wrong number.

  1. 1, 3, 9, 31, 128, 651, 3913
    1. 651
    2. 128
    3. 31
    4. 9
    5. 3
Correct Option: B

As per the details in the question the series is in the form of
Next term = ( Previous term × variable ) + ( 1 + variable )
First term = 1
Second term = First term × 1 + 2
Second term = 1 × 1 + 2 = 3 ;
Third term = Second term × 2 + 3
Third term = 3 × 2 + 3 = 9 ;
Similarly , we can find all others terms also.
Fourth term = Third term × 3 + 4
Fourth term = 9 × 3 + 4 = 31 ;
Fifth term = Fourth term × 4 + 5
Fifth term = 31 × 4 + 5 = 128 , is wrong . it should be 129 as fifth term .
Sixth term = Fifth term × 5 + 6
Sixth term = 129 × 5 + 6 = 651 ;
Seventh term = Sixth term × 6 + 7
Seventh term = 651 × 6 + 7 = 3913



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