Conditional probability problem for 5 red balls and 5 blue balls in a bag

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A bag contains 5 red balls and 5 blue balls. Three balls are drawn randomly without replacement.
Find: the conditional probability of drawing at least 1 blue ball if we had already drew at least one red ball.

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Probability = 2/3

According to the condition,
it is fixed that we had already drawn a red ball.
So we can say that - now we are left only with the possible combination from 2 balls.
These 2 balls can be in combination of

  • red-blue (or blue-red both are same)
  • red-red
  • blue-blue

    Only in 2 out of 3 combinations, we get at least 1 blue ball.

    (Just don't forget that we are ignoring the 3rd ball as it is already been told that it is red.)