There are two boxes, box 1 and box 2. Box 1 contains 9 red balls, 5 green balls and 2 blue balls, and box 2 contains 3 red balls, 2 green balls and unknown number of blue balls. If a box is chosen at random and a ball is drawn from it, the probability of getting a blue ball is at least 0.25. What is the minimum number of blue balls that should be there in box 2?

The total probability of drawing a blue ball is the sum of the probabilities from both boxes, calculated as 1/2 multiplied by (2/16) plus 1/2 multiplied by (b divided by the total in box 2). Setting this equation to be at least 0.25 gives 1/16 plus b divided by (2 times (5 plus b)) is greater than or equal to 1/4. Solving this inequality yields b is greater than or equal to 2.2. Since the number of blue balls must be a whole number, the minimum number of blue balls required is 3.

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