Answer :
You have the right idea. Let us define below events for ease of reference
R : use regular
E : use extra
P : use premium
F : full tank
Given info
P(R) = 0.4
P(E) = 0.35
P(P) = 0.25
P(F|R) = 0.3
P(F|E) = 0.6
P(F|P) = 0.5
a) This can be worked using conditional probability :
[tex]P(E{\cap}F)=P(E)*P(F|E)=0.35*0.6=\boxed{0.21}[/tex]
b) Since [tex]R,E,P[/tex] are pairwise disjoint events, we may use law of total probability to realize [tex]P(F)[/tex] :
[tex]P(F)=P(R{\cap}F)+P(E{\cap}F)+P(P{\cap}F)\\=P(R)*P(F|R)+P(E)*P(F|E)+P(P)*P(F|P)\\=0.4*0.3+0.35*0.6+0.25*0.5\\=\boxed{0.455}[/tex]
c) This can be worked using conditional proability too :
[tex]P(R'|F)=1-P(R|F)\\=1-\dfrac{P(R{\cap}F)}{P(F)}\\=1-\dfrac{P(R)*P(F|R)}{P(F)}\\=1-\dfrac{0.4*0.3}{0.455}\\=1-0.264\\=\boxed{0.736}[/tex]
R : use regular
E : use extra
P : use premium
F : full tank
Given info
P(R) = 0.4
P(E) = 0.35
P(P) = 0.25
P(F|R) = 0.3
P(F|E) = 0.6
P(F|P) = 0.5
a) This can be worked using conditional probability :
[tex]P(E{\cap}F)=P(E)*P(F|E)=0.35*0.6=\boxed{0.21}[/tex]
b) Since [tex]R,E,P[/tex] are pairwise disjoint events, we may use law of total probability to realize [tex]P(F)[/tex] :
[tex]P(F)=P(R{\cap}F)+P(E{\cap}F)+P(P{\cap}F)\\=P(R)*P(F|R)+P(E)*P(F|E)+P(P)*P(F|P)\\=0.4*0.3+0.35*0.6+0.25*0.5\\=\boxed{0.455}[/tex]
c) This can be worked using conditional proability too :
[tex]P(R'|F)=1-P(R|F)\\=1-\dfrac{P(R{\cap}F)}{P(F)}\\=1-\dfrac{P(R)*P(F|R)}{P(F)}\\=1-\dfrac{0.4*0.3}{0.455}\\=1-0.264\\=\boxed{0.736}[/tex]
We use the conditional probability rule: Kolomogorov definition.
P (A and B ) = P (A) * P (B | A)
a. 0.35 * 0.60 = 0.21
b. 0.40 * 0.30 + 0.35 * 0.60 + 0.25 * 50 = 0.455
c.
Using the conditional probability theorem :
P ( A | B) = prob that A occurs given that B has occurred.
= P (A Π B) / P (B), A Π B is the intersection of A & B events.
Here B = event that the next customer fills the tank
A = event that regular gas is not filled.
P(B) = prob that a customer fills the tank = 0.455, calculated above.
P(A) = probability that regular gas is not requested = 1 - 0.40 = 0.60
probability that regular gas is not requested and the customer fills the tank
P(A Π B) = 0.35 * 0.60 + 0.25 * 0.50 = 0.335
Required prob = 0.335 / 0.455 = 0.736
P (A and B ) = P (A) * P (B | A)
a. 0.35 * 0.60 = 0.21
b. 0.40 * 0.30 + 0.35 * 0.60 + 0.25 * 50 = 0.455
c.
Using the conditional probability theorem :
P ( A | B) = prob that A occurs given that B has occurred.
= P (A Π B) / P (B), A Π B is the intersection of A & B events.
Here B = event that the next customer fills the tank
A = event that regular gas is not filled.
P(B) = prob that a customer fills the tank = 0.455, calculated above.
P(A) = probability that regular gas is not requested = 1 - 0.40 = 0.60
probability that regular gas is not requested and the customer fills the tank
P(A Π B) = 0.35 * 0.60 + 0.25 * 0.50 = 0.335
Required prob = 0.335 / 0.455 = 0.736