một hộp bóng có 12 bóng đèn, trong đó có 7 bóng tốt, lấy ngẫu nhiên 3 bóng. tính xác suất để được: a) ít nhất 2 bóng tốt b) cả 3 bóng đều không tốt

To solve this problem, we can use the concept of probability. a) To find the probability of getting at least 2 good bulbs, we can use the formula for probability: $$ The total number of outcomes when selecting 3 bulbs from 12 is given by the combination formula: $$ The number of favorable outcomes for getting at least 2 good bulbs can be calculated by adding the combinations for selecting exactly 2 good bulbs and all 3 good bulbs: $$ b) To find the probability of getting all 3 bad bulbs, we can use a similar approach: $$ So, the final answers are: Probability of getting at least 2 good bulbs: $$ Probability of getting all 3 bad bulbs: $$