Two distinct numbers a and b are selected at random from 1, 2, 3, , 50. The probability, that their product ab is divisible by 3, is
- 2721225
- 5611225
- 6641225
- 825
Answer
(3) 6641225
Solution
Total ways = 50C2 = 50 492 = 1225
Multiples of 3 in 1 to 50: 3, 6, , 48 → 16 numbers
Non-multiples = 50 - 16 = 34
ab is not divisible by 3 both are non-multiples:
ways = 34C2 = 34 332 = 561
P(ab divisible by 3) = 1 - 5611225 = 6641225
Answer: (3)