Math Problem Statement

answer

Events A and B are independent. P(A) = 3/5 and P(A ∪ B) = 2/3. Find P(B|A). Give an exact answer as a fraction in fully simplified form.

Solution

To solve this problem, we need to find P(BA)P(B|A), which is the conditional probability of BB given AA.

Given:

  • P(A)=35P(A) = \frac{3}{5}
  • P(AB)=23P(A \cup B) = \frac{2}{3}
  • AA and BB are independent events.

Steps to Solve:

  1. Use the formula for the union of two events:

    P(AB)=P(A)+P(B)P(AB)P(A \cup B) = P(A) + P(B) - P(A \cap B)

    Since AA and BB are independent:

    P(AB)=P(A)P(B)P(A \cap B) = P(A) \cdot P(B)

    Substituting this into the union formula gives:

    P(AB)=P(A)+P(B)P(A)P(B)P(A \cup B) = P(A) + P(B) - P(A) \cdot P(B)

  2. Substitute the known values:

    23=35+P(B)(35P(B))\frac{2}{3} = \frac{3}{5} + P(B) - \left(\frac{3}{5} \cdot P(B)\right)

    Simplify the equation:

    23=35+P(B)(135)\frac{2}{3} = \frac{3}{5} + P(B) \left(1 - \frac{3}{5}\right)

    23=35+P(B)25\frac{2}{3} = \frac{3}{5} + P(B) \cdot \frac{2}{5}

    Multiply everything by 15 to eliminate the denominators:

    10=9+6P(B)10 = 9 + 6P(B)

    Subtract 9 from both sides:

    1=6P(B)1 = 6P(B)

    Therefore, P(B)=16P(B) = \frac{1}{6}.

  3. Find P(BA)P(B|A):

    P(BA)=P(AB)P(A)=P(A)P(B)P(A)=P(B)P(B|A) = \frac{P(A \cap B)}{P(A)} = \frac{P(A) \cdot P(B)}{P(A)} = P(B)

    Substituting the value of P(B)P(B):

    P(BA)=16P(B|A) = \frac{1}{6}

Final Answer:

P(BA)=16P(B|A) = \frac{1}{6}

Would you like more details, or do you have any further questions?

Here are five related questions for practice:

  1. If P(A)=0.7P(A) = 0.7 and P(B)=0.4P(B) = 0.4, and AA and BB are independent, what is P(AB)P(A \cap B)?
  2. Given that P(A)=0.5P(A) = 0.5, P(B)=0.3P(B) = 0.3, and P(AB)=0.65P(A \cup B) = 0.65, find P(AB)P(A \cap B).
  3. If P(AB)=0.9P(A \cup B) = 0.9 and P(AB)=0.2P(A \cap B) = 0.2, what is P(A)P(A) if P(B)=0.4P(B) = 0.4?
  4. What is the conditional probability P(AB)P(A|B) if P(B)=0.2P(B) = 0.2 and P(AB)=0.1P(A \cap B) = 0.1?
  5. How would the independence of events AA and BB affect the calculation of P(AB)P(A \cup B)?

Tip: When dealing with conditional probabilities, remember that the definition P(BA)=P(AB)P(A)P(B|A) = \frac{P(A \cap B)}{P(A)} can simplify many problems, especially when events are independent.

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Math Problem Analysis

Mathematical Concepts

Probability
Conditional Probability
Independent Events

Formulas

P(A ∪ B) = P(A) + P(B) - P(A ∩ B)
P(A ∩ B) = P(A) × P(B) for independent events
P(B|A) = P(A ∩ B) / P(A)

Theorems

Multiplication Rule for Independent Events
Conditional Probability Formula

Suitable Grade Level

Grades 10-12