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The series of natural number is divided ...

The series of natural number is divided into groups 1 , 2, 3, 4,...... and so on. Then the sum of the numbers in the nth group is

A

A.`(2n - 1)(n^2 - n + 1)`

B

B.`n^3 - 3n^2 + 3n -1`

C

C .`n^3 + (n - 1)^3`

D

D. `(n^3 + n)/2`

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The correct Answer is:
A, C
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