Given that
$$P(A) = 0.35 \quad P(B) = 0.45 \quad \text{and} \quad P(A \cap B) = 0.13$$
find
(a) \( P(A' | B') \) (2)
(b) Explain why the events A and B are not independent - Edexcel - A-Level Maths Statistics - Question 4 - 2017 - Paper 2
Question 4
Given that
$$P(A) = 0.35 \quad P(B) = 0.45 \quad \text{and} \quad P(A \cap B) = 0.13$$
find
(a) \( P(A' | B') \) (2)
(b) Explain why the events A and B are not i... show full transcript
Worked Solution & Example Answer:Given that
$$P(A) = 0.35 \quad P(B) = 0.45 \quad \text{and} \quad P(A \cap B) = 0.13$$
find
(a) \( P(A' | B') \) (2)
(b) Explain why the events A and B are not independent - Edexcel - A-Level Maths Statistics - Question 4 - 2017 - Paper 2
Step 1
Find \( P(A' | B') \)
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Answer
To find ( P(A' | B') ), we can use the formula:
P(A′∣B′)=1−P(A∣B)
First, we find ( P(A | B) ) using:
P(A∣B)=P(B)P(A∩B)=0.450.13≈0.2889
Now, substituting into our original formula:
P(A′∣B′)=1−0.2889≈0.7111
Step 2
Explain why the events A and B are not independent.
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Answer
Events A and B are not independent because:
P(A∩B)=P(A)⋅P(B)
Calculating, we find:
P(A∩B)=0.13andP(A)⋅P(B)=0.35⋅0.45=0.1575
Since ( 0.13 \neq 0.1575 ), the events are dependent.
Step 3
Draw a Venn diagram to illustrate the events A, B and C.
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Answer
In the Venn diagram:
Region for A only contains 0.22
Region for B only contains 0.09
Region for C only has 0.20
The overlap between A and B contains 0.13
The area A and C overlaps shows 0.00 since they are mutually exclusive.
Each region should be clearly labeled to show these probabilities.
Step 4
Find \( P(B \cup C') \)
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Answer
Using the formula for the union of two probabilities:
P(B∪C′)=P(B)+P(C′)−P(B∩C′)
We know:
( P(B) = 0.45 )
( P(C') = 1 - P(C) = 1 - 0.20 = 0.80 )
To find ( P(B \cap C') ), we use the independence state of B and C: