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Probability
· Formula🧮 Formula Reference Sheet
P(E) = Favourable outcomes ÷ Total outcomes P(A∪B) = P(A)+P(B)−P(A∩B) P(A|B) = P(A∩B)÷P(B) [Conditional] P(A∩B) = P(A)×P(B) [Independent] P(A') = 1 − P(A) [Complement]
⚡ Example per formula
P(E) = Favourable outcomes ÷ Total outcomes
↳Die rolled, P(>4) = 2/6 = 1/3
P(A∪B) = P(A)+P(B)−P(A∩B)
↳P(red)=4/10, P(king)=4/52, ∪ = 4/10+4/52−2/52
P(A|B) = P(A∩B)÷P(B) [Conditional]
↳Bag 5R 3G; P(green | not blue) = 3/8
P(A∩B) = P(A)×P(B) [Independent]
↳Two coins independent: P(HH) = ½ × ½ = 1/4
P(A') = 1 − P(A) [Complement]
↳P(at least one head, 3 tosses) = 1 − (1/2)³ = 7/8
✏️ Worked Example
A die is rolled once. What is the probability of getting an even number?
👁 Show step-by-step solution
Even outcomes: {2, 4, 6} = 3 outcomes
Total outcomes = 6
P(even) = 3/6 = 1/2
✅ Answer: 1/2✏️
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