A petrol attendant recorded the number of vehicles that bought petrol from him for -3 hours and recorded 12…

Analyze the question: The attendant recorded 12 cars and 27 buses. We want the probability that the next vehicle is a bus. (The "-3 hours" is just a typo for the time period and does not affect the calculation.)

Concept: Using observed data (relative frequency),

Probability = (number of favourable outcomes) / (total number of outcomes)

Solution:

• Number of buses = 27
• Total vehicles = 12 + 27 = 39

P(bus) = 27/39

Divide the top and bottom by 3:

P(bus) = 9/13

Answer: Option E, 9/13.

Check on the other options:

• 4/13 is the probability of a car (12/39 = 4/13), so B is the complement of the correct answer. This is a common trap.
• 4/39, 5/13 and 6/13 do not come from these figures.

Tip: Always add up all the outcomes to get the denominator, and reduce the fraction to its simplest form so you can match it to the options. A quick check is that P(car) + P(bus) must equal 1: 4/13 + 9/13 = 13/13 ✓.