I think OA is correct.

Total ways = 8P2 = 56

Ways when atleats oen of them is blue

BB - 2 cases (B1B2, B2B1)

BR - 4 cases (B1R1, B2R1, B1R2, B2R2)

RB - 4 cases

BY - 4 cases

YB - 4 cases

BG - 4 cases

GB - 4 cases

Total when atleast 1 is blue = 26

Total when none of them is blue = 30

Prob = 30/56 = 15/28

I think you forgot to take into account when one of them is blue. Question would be more clear if this would have been written "None of them is blue."

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SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008