WHY DID I TAKE MATHS AT A LEVEL
My C1 exam on Wednesday was completely awful and my S1 today was equally as bad. :/ Gonna retake loads.
S1: Probability Notation
P(AuB) (Union of A and B) = P(A) or P(B) or P(A and B)
P(AnB) (A intersection B) = P(A and B)
P(A’) (Not A) = 1 - P(A)
P(B’) (Not B) = 1 - P(B)
P(A’nB) (A’ intersection B) = P(A’ and B)
P(AnB’) (A intersection B’) = P(A and B’)
Addition rule
P(AuB) = P(A) + P(B) - P(AnB)
P(AnB) = P(A) + P(B) - P(AuB)
If mutually exclusive (cannot happen at the same time):
P(AuB) = P(A) + P(B) - 0
∴P(AuB) = P(A) + P(B)
Multiplication rule
P(A|B) = P(AnB)/P(B)
If independent (probability of an event doesn’t change if something else has happened):
P(AnB) = P(A) x P(B)
