Probability of Drawing Same-Colored Balls from a Box

In summary, the probability of drawing two balls of the same color from a box containing 2 red, 4 white, and 4 green balls without replacement is $\displaystyle{\frac{2}{10} \cdot \frac{1}{9}+\frac{4}{10} \cdot \frac{3}{9}+\frac{4}{10} \cdot \frac{3}{9}}$.
  • #1
rymatson406
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A box contains 2 red, 4 white, and 4 green two balls are drawn in succession without replacement. What is the probability that both balls are the same color?
 
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  • #2
rymatson406 said:
A box contains 2 red, 4 white, and 4 green two balls are drawn in succession without replacement. What is the probability that both balls are the same color?

The probability is the sum of the probabilities:
  • 1. ball red and 2. ball red
  • 1. ball white and 2. ball white
  • 1. ball green and 2. ball green

The probability "1. ball red and 2. ball red":

The probability to pick a red ball from the box which contains $10$ balls, where $2$ of them are red, is $\displaystyle{\frac{2}{10}}$.
Now there are $9$ balls left in the box and $1$ of them is red.
So the probability for the second ball to be red is $\displaystyle{\frac{1}{9}}$.

Therefore the probability "1. ball red and 2. ball red" is equal to $$\frac{2}{10} \cdot \frac{1}{9}$$Do the same for the two other cases, and you get:
$$\frac{2}{10} \cdot \frac{1}{9}+\frac{4}{10} \cdot \frac{3}{9}+\frac{4}{10} \cdot \frac{3}{9}$$
 
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Related to Probability of Drawing Same-Colored Balls from a Box

1. What is the probability of drawing two same-colored balls from a box?

The probability of drawing two same-colored balls from a box depends on the total number of balls in the box and the number of balls of each color. For example, if there are 10 red balls and 10 blue balls in the box, the probability of drawing two red balls would be (10/20) x (9/19) = 0.2368 or 23.68%.

2. How does the number of balls in the box affect the probability of drawing same-colored balls?

The number of balls in the box directly affects the probability of drawing same-colored balls. As the number of balls increases, the probability of drawing same-colored balls decreases. This is because there are more options to choose from, making it less likely to draw two balls of the same color.

3. What happens to the probability if we replace the drawn ball back into the box?

If the drawn ball is replaced back into the box, the probability of drawing same-colored balls remains the same for subsequent draws. This is known as sampling with replacement, where each draw is independent of the previous one.

4. Can the probability of drawing same-colored balls be greater than 50%?

Yes, the probability of drawing same-colored balls can be greater than 50%, depending on the number of balls of each color in the box. For example, if there are 20 red balls and only 1 blue ball in the box, the probability of drawing two red balls would be (20/21) x (19/20) = 0.9048 or 90.48%.

5. Is the probability of drawing same-colored balls affected by the order in which the balls are drawn?

No, the probability of drawing same-colored balls is not affected by the order in which the balls are drawn. This is known as sampling without replacement, where each draw affects the probability of the subsequent draws. However, as the number of draws increases, the impact of the order diminishes and the overall probability approaches a steady value.

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