Probability — O/L Mathematics

What must I remember about Probability?

• Probability of an event A with equally likely outcomes: P(A) = n(A) / n(S), where n(A) is favorable outcomes and n(S) is total sample space outcomes.
• Probability bounds: For any event A, 0 ≤ P(A) ≤ 1; impossible event P(∅) = 0; certain event P(S) = 1.
• Complementary events rule: P(A') = 1 - P(A); the probability of an event NOT happening equals 1 minus the probability that it happens.
• Two independent events: The sample space can be represented on a Cartesian grid or a probability tree diagram.
• Multiplication rule for independent sequential events along tree branches: P(A and B) = P(A) × P(B).

Test yourself (1 minute)

1. With replacement vs Without replacement

   In drawing problems, 'without replacement' reduces both the numerator and the denominator of the total items on the second draw.

2. Branch probability sum

   The sum of probabilities emanating from any single node on a tree diagram MUST always equal 1.

3. 'At least one' shortcut

   Calculate P(at least one success) = 1 - P(no successes) to save extensive branch additions.

Practise Probability questions today

Source: NIE G.C.E. (O/L) Mathematics Syllabus (Grade 10 & 11, Unit 29/25)

What should I study first?

Next in the syllabus

Where does Probability fit in the syllabus?

Grade 10 · Term 3 · Grade 11 · Term 3