Probabilities can be calculated from tables by determining the frequency of a specific event, and the total frequency for all events.
For example, a class determines how the students travel to school:
The probability that a student travels to school by car is the total for the cars column (7) divided by the total for all journeys to school (31). P(car) = `frac(7)(31)`.
The colour of each car entering a car park is noted. What is the probability of a car chosen at random being red?
There are 10 red cars. The probability of it being a red car is P(red) = `frac(10)(38)` = `frac(5)(19)`
The type of transport used by students to travel to school is noted below. What is the probability that a student will take a bus or a train to school?
All students are being considered: total frequency = 31
7 students (2 + 5) travel by bus; and 3 students (1 + 2) travel by train.
P(bus or train) = `frac(10)(31)`