natalia sivackova introduction to probability. equally likely events coin toss example: probability...
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NATALIA SIVACKOVA
Introduction to Probability
Equally Likely Events
Coin toss example:Probability of result is ½
Dice example:Probability of result is 1/6
For nth termProbability = 1/n
Not Equally Likely Events
Bag of marbles4 blue5 green6 red
Probability of picking blue?4/15
General Formula
The bag is Un(U) = 15
Blue marbles form a subset A UProbability of picking a member of A is P(A)
P(A) = n(A)/n(U)
Probability of a Complementary Event
Sock drawer contains 53 socks13 are single socks40 are in a pair
Probability of single sock: n(S)/n(U) = 13/53Probability of a sock from a pair: n(S’)/n(U) =
40/53
P(S) + P(S’) = 53/53 = 1
Generalized formula for all subsets: P(S’) = 1 – P(S)
S S’ = U
Cont.
When an event is certain it has a probability of 1When an event is impossible it has a probability
of 0
(e.g. of an impossible event)S S’ =
(You cannot pick a sock that is both single and part of a pair)
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