Discussion

Explanation:

For both the balls to be of different color, we need to pick either 

1 blue & 1 red = 5 × 6 = 30 ways.
1 red & 1 black = 6 × 4 = 24 ways
1 blue & 1 black = 5 × 4 = 20 ways.

∴ Number of ways of picking 2 balls of different color = 30 + 24 + 20 = 74 ways.

Now, total number of ways of picking 2 balls out of 15 = ¹⁵C₂ = 105

P (both the balls are of different color) = 74/105

Hence, option (b).

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