Intro to probability
On the probability line what word represents the number 0 and the number 1.
0=impossible
1=certain
1/2
What is the formula for relative frequency?
Relative Frequency = # of successful trials / total number of trials
What is A and A'. Give a formula that uses both.
1 = p(A) + p(A')
What is the formula of finding the # of times an event happens?
# of time the event happens = p x Total
Place these in order of least to most likely:
1) someone being 90 years old.
2) someone being 110 years old
3) someone being 20 years old.
2) someone being 110 years old
1) someone being 90 years old.
3) someone being 20 years old.
There are 3 chocolates, 2 mints, and 5 smarties in a bag. If you choose one at random, what is the probability of it not being a mint.
(3+5) / (3+2+5)
8/10 = 4/5
You roll a dice 20 times and get a 4, 8 times.
What's the relative frequency of getting the 4?
8/20 = 2/5
The probability of getting spelling correct on a test is 0.75. What's the probability of the wrong answer?
1-0.75=0.25
If you roll a dice 600 times, how many times do you expect to get an even number?
Prob of an even number = 1/2
600x(1/2) = 300
Where would these be on the probability line?
a) it will rain tomorrow.
b) a grade 7 student is 7 years old.
a) it will rain tomorrow. likely
b) a grade 7 student is 7 years old. unlikely
5/16
If it rained 12 days in November, what's the probability of it raining on 21st November?
2/5
What is the probability of not getting a prime number on a dice?
prime numbers: 2, 3, 5
not prime numbers: 1, 4, 6
3/6 = 1/2
The probability a person knows the Pythagorean theorem is 1/25. If there are 30,000, how many people will know the theorem.
Describe 2 events with an even chance.
coin toss heads or tails
a number being even or odd
There are 6 faces on a square. 3 are red, 2 are blue, and 1 is yellow.
If a face is chosen at random, what is the probability of it being red, blue, and yellow?
Red: 1/2
Blue: 1/3
Yellow: 1/6
Ali says the probability of a parking space being empty is 4/5. This is based on 50 days of observation. On how many days will a parking space not be empty?
RF = #successful trials / total
1/5 = #st / 50
#st = (1/5)x50
#st = 10
It rains 12 days in September. What is the probability it won't rain on a given day in September?
rain = 12/30
no rain = 18/30 = 9/15 = 3/5
The probability of winning a game is 3/5. If a person plays 15 games, how many does he lose?
lose = 1 - (3/5) = 2/5
(2/5)(15) = 6
Describe an event that's impossible, unlikely, even chance, likely, and certain.
Any
A bag has 6 red marbles and some white ones. If a marble is taken at random, the prob of red is 3/5. How many white marbles are there?
4
A team can either win, lose, or draw a game. If they play 20 games, win 5, and lose 4, what is the probability of a draw.
20 - (5+4) = 20-9=11
11/20
A bag has 100 soccer balls. Each soccer ball is marked 1 to 100 each. If a ball is picked at random. What is the probability of the ball being a multiple of 3?
33/100
The probability of missing the school bus is 1/10. In 4 weeks how many days does he miss the bus?
(1/10)(4x5)
(1/10)(20)
2