Probability Tables

Probability Tables

GCSE(F),

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:

WalkCarBikeBusTrainTotal
Girls5522115
Boys4235216
Total9757331

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)`.

Examples

1. The colour of each car entering a car park is noted. What is the probability of a car chosen at random being red?

WhiteRedBlueGreenBlackSilver
8?7535

Answer: `frac(1)(3)`

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?

WalkCarBikeBusTrainTotal
Girls5522115
Boys4235216
Total9757331

Answer: `frac(3)(10)`

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)`