What this guide covers
Selected Sec 2 S2 probability of single events. Two-stage draws, tree diagrams and independent-event calculations are later work.
Count outcomes, not distinct labels
Eight equal sectors are eight possible outcomes even if several carry the same number. A probability must lie from 0 to 1; the event and its complement together cover all outcomes.
Repeated labels on a spinner
A fair spinner has eight equal sectors labelled 1,1,2,2,2,3,3,4. Find the probability of an even number and of a number greater than 2.
- There are eight equally likely sectors. Even labels occupy three 2-sectors and one 4-sector: 4 outcomes, so P(even)=48=12.
- Labels greater than 2 occupy two 3-sectors and one 4-sector: 3 outcomes, so P(>2)=38.
Check: The labels are not four equally likely numbers; the repeated sectors must each be counted.
Try it yourself
Work on paper, then compare the steps. These checks do not establish mastery.
A fair six-sided die is rolled once. What is the probability of a prime number?
Prime outcomes are 2, 3 and 5: 3 of 6 equally likely faces. Probability =36=12. The number 1 is not prime.
A box contains 5 green, 3 yellow and 2 blue identical counters. One is selected at random. Find the probability that it is not yellow.
Total =5+3+2=10. Not yellow means green or blue: 5+2=7 outcomes, so probability =710. Equivalently, 1−310=710.
Where this connects
- Related: interpreting data →
Observed frequencies describe a sample; probabilities describe modelled chance.
- Later: combined events →
The Upper Secondary guide follows more than one random step.
Sources and scope
Original Mentora spinner and counter tasks aligned to selected Sec 2 S2 content in the MOE G2/G3 Mathematics syllabus. No third-party spinner graphic or question was used.