A box contains 7 red balls, 8 green balls and 5 blue balls. When one ball is randomly drawn from the box, probability of its bein…

Question

A box contains 7 red balls, 8 green balls and 5 blue balls. When one ball is randomly drawn from the box, probability of its being a blue ball will be:

1. A. 1/2
2. B. 1/3
3. C. 1/4 (Correct answer)
4. D. 1/5

Correct Answer

Option C — 1/4

Detailed Solution & Explanation

The correct answer is 1/4.

Key Points

• Total balls = 7 red + 8 green + 5 blue = 20.
• Favourable outcomes (blue) = 5.
• Probability = 5/20 = 1/4.

Additional Information

• Always compute the total first; using only the blue and one other colour is the usual slip.
• The complementary probability, that the ball is not blue, is 1 − 1/4 = 3/4, matching the 15 non-blue balls out of 20.
• For draws without replacement, the denominator falls by one each time — a distinction that matters as soon as a second ball is drawn.