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If, for a positive integer n , the quadr...

If, for a positive integer `n ,` the quadratic equation, `x(x+1)+(x-1)(x+2)++(x+ n-1)(x+n)=10 n` has two consecutive integral solutions, then `n` is equal to : `10` (2) `11` (3) `12` (4) `9`

A

11

B

12

C

9

D

10

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The correct Answer is:
A
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