Probability How likely it is that something will happen.

p: symbol to represent the probability of a particular outcome.

# of ways an event can occur p = total # of events

The event: rolling a 3 with one die 1 (# of ways the event occurs) p = 6 ( total # of possible events)

Event: rolling a 5 with a pair of dice # of ways the event can occur:

Total # of events :

Probability of rolling 5 with a pair of dice 4 (# of ways the event can occur) p = 36 (total number of events) 1 p= p =.11 9

All events: 50 pieces of paper 10 green 20 red 15 yellow 5 blue (papers are returned after each draw)

1) Prob. of two events both occurring Event A and Event B ( Prob. A) (Prob. B)

Event: drawing a red and a yellow

All events: 50 pieces of paper 10 green 20 red 15 yellow 5 blue (papers are returned after each draw)

Event: drawing a red and a yellow prob of red and prob of yellow

or: p =.12

Probability does not have memory ! If the event is defined as two draws then this method applies. If the event is limited to the second draw only, the probability is based on that event alone

2) The probability of either of two mutually exclusive events occurring is the sum of their probabilities. Prob A or Prob B (Prob A ) + (Prob B)

Event: in one draw, choosing a yellow or red.

All events: 50 pieces of paper 10 green 20 red 15 yellow 5 blue (papers are returned after each draw)

Event: in one draw, choosing a yellow or red p =.7

Mutually Exclusive: When two events can not co- occur.

Events that are not mutually exclusive: Using a standard deck of 52 playing cards, Drawing a face card or a heart. 12 faces cards 13 hearts 3 cards that are face cards and hearts

Prob A + Prob B - (Prob AB)