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 (30). P(car) = `frac(7)(30)`.
1. 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. There are 30 cars in total. P(red) = `frac(10)(30)` = `frac(1)(3)`
2. 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 = 30
6 students (2 + 4) travel by bus; and 3 students (1 + 2) travel by train.
P(bus or train) = `frac(9)(30)` = `frac(3)(10)`