What is the probability of picking a red ball twice from a bag of 6 blue balls and 3 red balls, without replacement.

The probability of picking a ball from a bag is the number of balls of that colour divided by the total number of balls.

Therefore in the first instance, the probability of a red ball is 3/9 or 1/3rd.

If that ball is now removed the probability of picking a 2nd is 2/8 or 1/4.

Therefore the probability that both these happen is 1/4 * 1/3 which is 1/12.