3.1.1
Random experiments and sample spaces
Learning objectives
- Define experiment, outcome, sample space, and event
- enumerate finite spaces without double counting
- distinguish a model from observations.
Worked examples
Worked example 1
Two ordered coin tosses: Ω={HH,HT,TH,TT}; exactly one head is {HT,TH}, so under a fair independent model P=2/4=1/2.
Worked example 2
Sum of two fair dice is not uniform: sum 2 has one ordered pair, sum 7 has six, so probabilities 1/36 and 6/36.
Common mistake and counterexample
“Six possible sums means each has probability 1/11” confuses distinct values with equally likely elementary outcomes.
Knowledge check and mastery evidence
4/4: define Ω/event, enumerate an ordered space, calculate a complement, and state assumptions; assumption statement mandatory. Connects to event algebra.