Math Problem Statement

The tree diagram below is general for events A and B where event B follows event A. Use the frequencies in the table to calculate the probabilities. Enter the probabilities in the table and determine if events A and B are independent.

Solution

Based on the image provided, we are working with a tree diagram and probabilities table for events AA and BB. Let’s break this down step by step:

1. Extract Information from the Table:

The table below the diagram shows counts for combinations of A,A,B,BA, A', B, B':

  • AB=21A \cap B = 21,
  • AB=18A \cap B' = 18,
  • AB=24A' \cap B = 24,
  • AB=57A' \cap B' = 57.

2. Calculate Total Outcomes:

Sum all values: Total=21+18+24+57=120.\text{Total} = 21 + 18 + 24 + 57 = 120.

3. Fill in the Probabilities:

  • P(A)P(A): Probability of event AA: P(A)=Number of outcomes in ATotal outcomes=21+18120=39120=0.325.P(A) = \frac{\text{Number of outcomes in } A}{\text{Total outcomes}} = \frac{21 + 18}{120} = \frac{39}{120} = 0.325.

  • P(A)P(A'): Complement of P(A)P(A): P(A)=1P(A)=10.325=0.675.P(A') = 1 - P(A) = 1 - 0.325 = 0.675.

  • P(B)P(B): Probability of event BB: P(B)=Number of outcomes in BTotal outcomes=21+24120=45120=0.375.P(B) = \frac{\text{Number of outcomes in } B}{\text{Total outcomes}} = \frac{21 + 24}{120} = \frac{45}{120} = 0.375.

  • P(B)P(B'): Complement of P(B)P(B): P(B)=1P(B)=10.375=0.625.P(B') = 1 - P(B) = 1 - 0.375 = 0.625.

  • P(BA)P(B | A): Conditional probability of BB given AA: P(BA)=P(AB)P(A)=211200.325=2139=0.538.P(B | A) = \frac{P(A \cap B)}{P(A)} = \frac{\frac{21}{120}}{0.325} = \frac{21}{39} = 0.538.

  • P(BA)P(B | A'): Conditional probability of BB given AA': P(BA)=P(AB)P(A)=241200.675=2481=0.296.P(B | A') = \frac{P(A' \cap B)}{P(A')} = \frac{\frac{24}{120}}{0.675} = \frac{24}{81} = 0.296.

  • P(B)AP(B') | A: Probability of BB' given AA: P(BA)=1P(BA)=10.538=0.462.P(B' | A) = 1 - P(B | A) = 1 - 0.538 = 0.462.

  • P(B)AP(B') | A': Probability of BB' given AA': P(BA)=1P(BA)=10.296=0.704.P(B' | A') = 1 - P(B | A') = 1 - 0.296 = 0.704.

4. Test for Independence:

For AA and BB to be independent, P(BA)=P(B)P(B | A) = P(B). Since P(BA)=0.538P(B | A) = 0.538 and P(B)=0.375P(B) = 0.375, they are not independent because these values are not equal.


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Math Problem Analysis

Mathematical Concepts

Probability
Conditional Probability
Independence of Events
Tree Diagrams

Formulas

P(A) = (Number of outcomes in A) / (Total outcomes)
P(A') = 1 - P(A)
P(B) = (Number of outcomes in B) / (Total outcomes)
P(B') = 1 - P(B)
P(B | A) = P(A ∩ B) / P(A)
P(B | A') = P(A' ∩ B) / P(A')
P(B') | A = 1 - P(B | A)
P(B') | A' = 1 - P(B | A')

Theorems

Independence of Events: Two events A and B are independent if P(B | A) = P(B).

Suitable Grade Level

Grades 10-12 (IB Math Studies/Analysis & Approaches)