A box contains 3 red balls, 2 blue balls, and 5 green balls. Two balls are drawn at random without replacement. What is the probability that both balls are green?
1/9
2/9
5/18
5/9
Show the answer and explanation
Correct answer
B. 2/9
Principle or equation
Probability of drawing two green balls without replacement: (number of green / total) * (number of green - 1) / (total - 1).
Why this answer is correct
Total balls = 10. Probability first green = 5/10 = 1/2. After one green removed, there are 4 green left out of 9. So probability = (1/2) * (4/9) = 4/18 = 2/9.
Example
If there are 4 red and 6 blue, probability of two reds = (4/10)*(3/9)=12/90=2/15.
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