Calculating the Probability of Selecting a Blue Marble

Oct 13, 2025 by pinkandtrash.com 80 views

Introduction

When dealing with probability problems, it's essential to understand the concept of independent events and how they affect the overall probability. In this scenario, we have a bag containing four blue marbles, an unknown number of red marbles, and six yellow marbles. We want to find the probability of randomly selecting a blue marble, replacing it, and then randomly selecting a red marble.

Understanding the Problem

To solve this problem, we need to break it down into two separate events: selecting a blue marble and selecting a red marble. Since we are replacing the blue marble after selecting it, the probability of selecting a blue marble remains constant for each draw. However, the probability of selecting a red marble depends on the number of red marbles in the bag.

Calculating the Probability of Selecting a Blue Marble

The probability of selecting a blue marble is the number of blue marbles divided by the total number of marbles in the bag. Since there are four blue marbles and a total of 10 marbles (4 blue + r red + 6 yellow), the probability of selecting a blue marble is:

P(blue) = 4 / (4 + r + 6)

Calculating the Probability of Selecting a Red Marble

After selecting a blue marble and replacing it, the probability of selecting a red marble is the number of red marbles divided by the total number of marbles in the bag. Since there are r red marbles and a total of 10 marbles (4 blue + r red + 6 yellow), the probability of selecting a red marble is:

P(red) = r / (4 + r + 6)

Finding the Overall Probability

To find the overall probability of selecting a blue marble and then a red marble, we need to multiply the probabilities of each event:

P(blue and red) = P(blue) * P(red)

Substituting the expressions for P(blue) and P(red), we get:

P(blue and red) = (4 / (4 + r + 6)) * (r / (4 + r + 6))

Simplifying the Expression

To simplify the expression, we can cancel out the common factors in the numerator and denominator:

P(blue and red) = (4r) / ((4 + r + 6)^2)

P(blue and red) = (4r) / ((10 + r)^2)

Conclusion

In conclusion, the expression that represents the probability of randomly selecting a blue marble, replacing it, and then randomly selecting a red marble is:

(4r) / ((10 + r)^2)

This expression takes into account the number of red marbles in the bag and provides a general formula for calculating the probability of this specific sequence of events.

Discussion

This problem requires a deep understanding of probability concepts, including independent events and the multiplication rule. It also highlights the importance of considering the number of red marbles in the bag when calculating the probability of selecting a red marble.

Example Use Case

Suppose we have a bag with 4 blue marbles, 5 red marbles, and 6 yellow marbles. We want to find the probability of randomly selecting a blue marble, replacing it, and then randomly selecting a red marble. Using the expression we derived earlier, we can plug in the values:

(4r) / ((10 + r)^2)

Substituting r = 5, we get:

(4(5)) / ((10 + 5)^2)

(20) / ((15)^2)

(20) / (225)

(4/9)

Therefore, the probability of randomly selecting a blue marble, replacing it, and then randomly selecting a red marble is 4/9.

Final Thoughts

In conclusion, this problem requires a thorough understanding of probability concepts and the ability to apply them to real-world scenarios. By breaking down the problem into smaller events and using the multiplication rule, we can derive a general expression for calculating the probability of this specific sequence of events.

Introduction

In our previous article, we explored the concept of probability and how to calculate the probability of randomly selecting a blue marble, replacing it, and then randomly selecting a red marble. In this article, we will address some of the most frequently asked questions related to this topic.

Q&A

Q: What is the probability of selecting a blue marble if there are 4 blue marbles and 10 total marbles in the bag?

A: The probability of selecting a blue marble is the number of blue marbles divided by the total number of marbles in the bag. In this case, the probability is:

P(blue) = 4 / 10 = 2/5

Q: What is the probability of selecting a red marble if there are 5 red marbles and 10 total marbles in the bag?

A: The probability of selecting a red marble is the number of red marbles divided by the total number of marbles in the bag. In this case, the probability is:

P(red) = 5 / 10 = 1/2

Q: How do I calculate the probability of selecting a blue marble and then a red marble if there are 4 blue marbles, 5 red marbles, and 6 yellow marbles in the bag?

A: To calculate the probability of selecting a blue marble and then a red marble, we need to multiply the probabilities of each event:

P(blue and red) = P(blue) * P(red)

Substituting the expressions for P(blue) and P(red), we get:

P(blue and red) = (4 / 10) * (5 / 10)

P(blue and red) = (4/10) * (1/2)

P(blue and red) = 2/10

P(blue and red) = 1/5

Q: What if I want to find the probability of selecting a blue marble and then a red marble if there are 4 blue marbles, 6 red marbles, and 6 yellow marbles in the bag?

A: To calculate the probability of selecting a blue marble and then a red marble, we need to multiply the probabilities of each event:

P(blue and red) = P(blue) * P(red)

Substituting the expressions for P(blue) and P(red), we get:

P(blue and red) = (4 / 16) * (6 / 16)

P(blue and red) = (1/4) * (3/8)

P(blue and red) = 3/32

Q: Can I use the same formula to calculate the probability of selecting a blue marble and then a red marble if there are 4 blue marbles, 5 red marbles, and 10 yellow marbles in the bag?

A: Yes, you can use the same formula to calculate the probability of selecting a blue marble and then a red marble. The formula is:

P(blue and red) = P(blue) * P(red)

Substituting the expressions for P(blue) and P(red), we get:

P(blue and red) = (4 / 19) * (5 / 19)

P(blue and red) = (4/19) * (5/19)

P(blue and red) = 20/361

Q: What if I want to find the probability of selecting a blue marble and then a red marble if there are 4 blue marbles, 6 red marbles, and 10 yellow marbles in the bag?

A: To calculate the probability of selecting a blue marble and then a red marble, we need to multiply the probabilities of each event:

P(blue and red) = P(blue) * P(red)

Substituting the expressions for P(blue) and P(red), we get:

P(blue and red) = (4 / 20) * (6 / 20)

P(blue and red) = (1/5) * (3/10)

P(blue and red) = 3/50

Conclusion

In conclusion, the probability of selecting a blue marble and then a red marble depends on the number of blue marbles, red marbles, and total marbles in the bag. By using the multiplication rule and the expressions for P(blue) and P(red), we can calculate the probability of this specific sequence of events.

Final Thoughts

In this article, we addressed some of the most frequently asked questions related to the probability of selecting a blue marble and then a red marble. We hope that this article has provided you with a better understanding of this concept and how to apply it to real-world scenarios.