Download Probability of a single event

1.2 Probability of a Single Event
Sample space – Total possible outcomes.
Probability of an Event
=
Number of Favorable outcomes
Number of total possible outcomes
Ex. Probability you roll a “6” on a standard 6 sided die.

Ex. Probability you flip a head if you flip a coin.
Probability is always a fraction. A “sure thing” has a probability of 1.
Ex. What is the probability of having a boy or a girl if you are having a baby?
Events that add up to 1 are “complementary events”.
Another way of asking the above is “Probability the baby is a girl or not a girl”.
Ex. You have 8 beads, 2 red, 3 blue and 3 white. What is the probability that a
bead selected at random is red?
Not red?
Probability that the bead is red or not red?
For any event A
P(A) + P(A) = 1
A and A are
“complementary
events”
1
Ex:
Roll a 6 sided die: P(5)=
5
1
P(even) =
2
2
3
6
3
Roll two dice:
How many outcomes in the sample space? _____
P( sum of 8)=
4
5
6
P( sum greater than 4)=
Single event probabilities may involve combinations: (ex picking a group of
cards or a handful of beads, etc)
Ex. What is the Probability that I am dealt a 5 card hand that contains 3 Aces and
2 Jacks?
What is the probability that I am dealt a 5 card hand that contains no hearts?
What is the probability that my 5 card hand contains at least one heart?
(**Use complementary events. Anything other that “no hearts” is “at least one
heart”, so you can use 1-P(no ) = P(at least one )
Ex. If I have a jar of 5 red, 6 blue and 10 green beads, what is the probability that
I choose 6 beads in such a way that I have 3 blue and 3 green beads?
Ex. What is the probability of getting 3 correct numbers in Lotto 6-49?
Of winning?
4
Single event probabilities may involve permutations (ex, letters, numbers or
other objects arranged at random).
Ex. The letters Y, M, O, E, and N are arranged randomly. What is the probability
that they are arranged to spell “Money”?
What is the probability that they do not spell the word “money”?
What is the probability that they are arranged with consonants and vowels
alternating?
Ex. Eight Math B30 students go to the Movie Theatre and sit in one row. If they
are seated in a random order, what is the probability that Darcy and Jane sit side
by side?
P = # ways Darcy and Jane can sit side by side
Total # ways to arrange 8 people
Rosengren, Melissa. (2008). Math Lessons. Estevan Sk