4.5 Trials, Events, Sample Space, Outcomes

Key ideas

• The vocabulary of trial, outcome, equally likely outcomes, relative frequency, sample space and event is used to discuss and explain events of chance.

• I can explain what complementary events are

• I can use the basic rules of probability to estimate likelihood of theoretical as well as everyday events

Experimental probability 

Experimental probability has to do with relative frequency.  If we measure or count how often a certain outcome occurs (the frequency) then we know the probability for that outcome. E.g. if you drop 1000 push pins and 318 land with the pointy end upwards, then the probability that a push pin lands with the pointy end up is 318/1000.

Sample space

In this lesson you are reminded about Sample Space:  The set of possible outcomes of a chance experiment.  There are various ways to describe the sample space:

1. In a list ( e.g. the sample space for tossing two coins {HH, HT, TH, TT}. Use proper set notation when you do this)

2. In a 2 dimensional grid (e.g. the outcomes of rolling two dice)

3. In a Tree diagram

Theoretical probability

Theoretical probability is the fraction of the number of interesting outcomes and the total number of possible outcomes of an experiment.  This is the very basis of ANY probability.  E.g. suppose we're interested in the outcome "A" occurring, then: