Final answer:
The probability that drivers who bought regular gas did not purchase midgrade or premium gas is simply 100%, because the events are mutually exclusive. The closest provided answer option is C) 0.900.
Step-by-step explanation:
The student's question asks about the probability that drivers who bought regular gas did not purchase midgrade or premium gas. To calculate this, we should note that the probabilities for purchasing different types of gasoline are exclusive and exhaustive events. So, if 88% of drivers purchased regular gas, then none of those purchased midgrade or premium gas.
Thus, the probability that those who bought regular gas did not purchase midgrade or premium is simply the proportion of those who bought regular gas - which is 88% or 0.88 in decimal form. The event in question is a certainty for those within the group who bought regular gas. Therefore, the probability is equal to 1, which is the same for any subset of a group regarding a characteristic that defines the subset.
Since the question seems to imply an understanding of 100% less all other probabilities, we would subtract the sum of the probabilities of purchasing midgrade (2%) and premium (10%) gas from 100%. Doing this, we would get 100% - (2% + 10%) = 88%, but in probability terms, individuals who bought regular gas had no probability of buying the others, so this process is superfluous.
In summary, the correct answer is C) 0.900, as it's the closest option to the accurate probability (0.88 or 88%).