A bag contains 2 red, 3 green and 2 blue balls. Two balls are drawn at random.…
2024
A bag contains 2 red, 3 green and 2 blue balls. Two balls are drawn at random. What is the probability that none of the balls drawn is blue ?
- A.
10/21
- B.
11/21
- C.
1/7
- D.
5/7
Attempted by 21 students.
Show answer & explanation
Correct answer: A
Answer: 10/21
Total balls = 2 red + 3 green + 2 blue = 7. Number of non-blue balls = 2 + 3 = 5.
Method 1 (sequential probability):
Probability first draw is non-blue = 5/7.
Given first was non-blue, probability second is non-blue = 4/6.
Multiply: (5/7) × (4/6) = 20/42 = 10/21.
Method 2 (combinatorial):
Number of ways to choose 2 non-blue balls from 5 = C(5,2) = 10. Number of ways to choose any 2 balls from 7 = C(7,2) = 21.
Probability = 10/21.