Answer:
Remember that for an event with a percentage probability X, the probability is given by:
P = X/100%
a) What is the probability that the next customer will request plus gas and fill their tank ?
We know that 35% of the customers use plus gas, and of these using plus, 20% fill their tank.
So the probability that the next customer uses plus gas is:
p = 35%/100% = 0.35
And the probability that the customer fills the tank (given that the customer uses plus gas) is:
q = 20%/100% = 0.2
The joint probability is just the product between the individual probabilities:
Then the probability that the next customer uses plus gas and fills their tank is:
P = 0.35*0.2 = 0.07
b) What is the probability that the next customer fills the tank?
We know that 20% of the ones that use plus gas (with a probability of 0.35) fill their tank, 10% of these that use regular gas (with a probability of 0.4) and 30% of these that use premium (with a probability of 0.25) fill their tank,
Then the probability is computed in a similar way than above, here the probability is:
P = 0.2*0.35 + 0.1*0.4 + 0.3*0.25 = 0.185
The probability that the next customer fills the tank is 0.185
c) If the next customer fills the tank, what is the probability that the regular gas is requested?
Ok, now we already know that the customer fills the tank.
The probability that a customer uses regular and fills the tank, is
p = 0.1*0.4
The probability that a customer fills the tank is computed above, this is:
P = 0.185
The probability, given that the customer fills the tank, the customer uses regular gas, is equal to the quotient between the probability that the customer fills the tank with regular and the probability that the customer fills the tank, this is:
Probability = p/P = (0.1*0.4)/(0.185) = 0.216
