In: Statistics and Probability
b. Suppose P(A) = 1 4 and P(B) = 2 5 .
(a) What is the maximum value of P(A ∩ B)?
(b) What is the minimum value of P(A ∩ B)? (
c) What is the maximum value of P(A ∩ B0 )
(d) What is the minimum value of P(A ∩ B0 )
(e) What is the maximum value of P(A ∪ B)?
(f) What is the minimum value of P(A ∪ B)?
(g) What is the maximum value of P(A|B)?
(h) What is the minimum value of P(A|B)?
P(A) = 1/4
P(B) = 2/5
(a)
Maximum value of P(A ∩ B) is the least of P(A) and P(B).
Therefore, Maximum value of P(A ∩ B) = 1/4
(b)
Minimum value of P(A ∩ B) is 0. It occurs when A and B are disjoint.
(c)
Maximum value of P(A ∩ B0 ) is the least of P(A) and P(B0).
P(B0) = 1- P((B)
= 3/5
Therefore, Maximum value of P(A ∩ B0 ) = 1/4
(d)
Minimum value of P(A ∩ B0 ) is 0. It occurs when A and B0 are disjoint.
(e)
Maximum value of P(A ∪ B) is P(A) + P(B)
We have, P(A ∪ B) = P(A) +P(B) - P(A ∩ B)
This is maximum when P(A ∩ B) is minimum, i.e when P(A ∩ B) is 0
Therefore, Maximum value of P(A ∪ B) = 1/4 + 2/5
= 13/20
(f)
Minimum value of P(A ∪ B) is the highest of P(A) and P(B)
Therefore, minimum value of P(A ∪ B) = 2/5
(g)
Maximum value of P(A|B) :
P(A|B) = P(A ∩ B)/P(B)
This is maximum when P(A ∩ B) is maximum
Therefore, Maximum value of P(A|B) = (1/4)/(2/5)
= 5/8
(h)
Minimum value of P(A|B) :
P(A|B) = P(A ∩ B)/P(B)
This is minimum when P(A ∩ B) is minimum
Therefore, minimum value of P(A|B) = 0