ACT Math : Probability
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Example Questions
Example Question #61 : How To Find The Probability Of An Outcome
When two dice are thrown, remember that the total number of oucomes is 
Now, for the data given, we know that the following pairs will work:
Thus, there are 
Example Question #171 : Data Analysis
If a person is born in the month of January, what is the probability they are born on a day that is divisible by 
To find the probability, divide the number of outcomes that fit the event description by the total possible number of outcomes. There are 31 days in January, so that is our denominator. Of those, 3,6,9,12,15,18,21,24,27,30 are divisble by three, which is 10 of the days. Thus the answer is:
Example Question #63 : How To Find The Probability Of An Outcome
There is a 
The total number of outcomes that fit the event (rolling a prime number) are the number of primes below 10: 2, 3, 5, 7 for a total of 4.
divide that but the total number of outcomes (10) and reduce:
Example Question #64 : How To Find The Probability Of An Outcome
You are trying to guess your friend's favorite day of the week. You know it's not a day that begins with "t". What is the chance that you guess correctly on your first try? Leave your answer as a simplified fraction.
There are 2 days that begin with "t". We know those cannot be the days. Since you are guessing you can only guess 1 outcome. The chance that that day is the corect one is the number of ways you can get it right (1, by guessing it right the first time) divide by the total number of outcomes (5).
Example Question #61 : How To Find The Probability Of An Outcome
There is an urn with three red balls, four green balls, and seven white balls in it. If you draw out a single ball, what is the probability that you don't pull out a red ball?
To find the probability of an event, divide the number of ways the event can happen by the total number of outcomes.
There are 11 balls that are not red, so there are 11 ways there can be a not red ball picked.
There are 14 balls total in the urn so the probability we pick a not red ball is:
Example Question #62 : How To Find The Probability Of An Outcome
You are rolling a 20 sided die. What is the probability that you roll a multiple of 6 when rolling the die? Simplify any fractions in your answer.
Divide the total number of ways to get the desire event by the total number of outcomes.
Since it is a 20 sided die there are 20 outcomes possible, but only 6, 12, and 18 are divisible by 6.
Thus, the probability that you roll a number divisible by 6 is:
Example Question #61 : Outcomes
When rolling a ten sided die, what is the probability you roll an even number? Leave your answer as a reduced fraction.
To find the probability find the total number of ways to get the described event (rolling an even number: 2,4,6,8,10 for a total of 5) divided by the total number of outcomes (10). Thus the answer is:
Remember to reduce the fraction!
Example Question #181 : Data Analysis
If you draw a single card from a standard deck of cards, what is the probability that you draw a face-card that is also a diamond (face-cards do not include 
To find the probability of an event, find the total number of ways the event can happen and divide that by the total number of outcomes. There are only 
Example Question #61 : How To Find The Probability Of An Outcome
Ilene has a bag of gum drops and a bag of gummy bears. The bag of gum drops contains 23 gum drops in the following colors: 3 red, 3 orange, 4 brown, 4 green, 6 blue and 3 yellow. The bag of gummy bears contains 26 gummy bears in the following colors: 4 red, 6 orange, 5 purple, 3 green, 5 yellow and 3 pink. If she dumps all of the gum drops and gummy bears into one bag, what is the probability that she will pick up either a red or green gum drop or gummy bear?
7/14
2/7
2/47
3/49
1/7
2/7
The total number of gum drops and gummy bears is 49. There are 7 red gum drops and gummy bears and 7 green gum drops and gummy bears. There is a 2 in 7 probability that you will pick up a green or red gum drop or gummy bear.
If you answered 1/7, then you only accounted for choosing either red gum drop or gummy bear or green ones.
If you answered 2/47 then you did not add the number of gum drops and gummy bears correctly.
If you answered 7 in 14 then you found the number of red or green gummy bears/gum drops out of the total red and green gummy bears and gum drops.
And if you answered 3 out of 49, you found only the probability of choosing either red gum drops or green gummy bears.
Example Question #181 : Data Analysis
Kaleah was born on the 17th day of the month. What is the probability that the next person she meets was born the 17th day of the month if they were born in August?
To find the probability of an event, find the number of ways that even can happen divided by the total number of possible outcomes.
There are 31 days in August, thus the total number of outcomes for someone being born in August is 31.
Since we only care about the event that is being born on the 17th, there is only one way that event can happen (being born on August 17th).
Thus the probability is
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