Let event [tex]\( B \)[/tex] be choosing a black ball first and event [tex]\( R \)[/tex] be choosing a red ball second.

What are the following probabilities?

[tex]\[
\begin{array}{l}
P(B) = \square \\
P(R \mid B) = \square \\
P(B \cap R) = \square
\end{array}
\][/tex]

The probability that the first ball chosen is black and the second ball chosen is red is about [tex]\(\square\)[/tex] percent.



Answer :

Certainly! Let's tackle each part of the problem step-by-step.

First, let's define the events:
- Let event [tex]\( B \)[/tex] be choosing a black ball first.
- Let event [tex]\( R \)[/tex] be choosing a red ball second, given that the first ball chosen was black.

1. Probability of choosing a black ball first, [tex]\( P(B) \)[/tex]:

The probability [tex]\( P(B) \)[/tex] represents the likelihood of selecting a black ball on the first draw. Given our information, we determine that:
[tex]\[ P(B) = \frac{7}{12} \approx 0.5833 \][/tex]

2. Conditional probability of choosing a red ball second, given that the first ball was black, [tex]\( P(R \mid B) \)[/tex]:

Given that the first ball chosen was black, the probability [tex]\( P(R \mid B) \)[/tex] indicates the likelihood of picking a red ball on the second draw. After drawing the first black ball, there are fewer total balls and black balls available. Thus:
[tex]\[ P(R \mid B) = \frac{5}{11} \approx 0.4545 \][/tex]

3. Joint probability of both events happening, [tex]\( P(B \cap R) \)[/tex]:

The joint probability [tex]\( P(B \cap R) \)[/tex] represents the likelihood of choosing a black ball first and then a red ball second. We calculate this by multiplying the individual probabilities:
[tex]\[ P(B \cap R) = P(B) \times P(R \mid B) \][/tex]
Substituting the values we determined:
[tex]\[ P(B \cap R) = 0.5833 \times 0.4545 \approx 0.2652 \][/tex]

4. Converting the joint probability to a percentage:

To express the probability that the first ball chosen is black and the second ball chosen is red as a percentage, we multiply by 100:
[tex]\[ \text{Percentage Probability} = P(B \cap R) \times 100 \approx 26.52\% \][/tex]

Summarizing all these probabilities:

[tex]\[ \begin{array}{l} P(B) = 0.5833 \\ P(R \mid B) = 0.4545 \\ P(B \cap R) = 0.2652 \end{array} \][/tex]

Therefore, the probability that the first ball chosen is black and the second ball chosen is red is about [tex]\( 26.52\% \)[/tex].