ISEE Lower Level Math : How to find the probability of an outcome
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Example Questions
Example Question #21 : How To Find The Probability Of An Outcome
Jen has a bag of 16 marbles. In the bag, there are 8 green marbles, 4 white, and 4 red marbles. If Jen reaches in and randomly chooses a marble, what is the probability (expressed as a percentage) that she chooses a white marble?
The chance of choosing a white marble is 
Example Question #22 : How To Find The Probability Of An Outcome
Use the diagram to answer the question.
If one of the shapes is chosen at random, what is the probability that it is a black circle?
1 out of 8
1 out of 5
1 out of 6
1 out of 12
1 out of 4
1 out of 6
To find the probability, we use a fraction:
There are 12 total shapes, and 2 black circles:
Reduce:
Thus, the probability is 1 out of 6.
Example Question #23 : How To Find The Probability Of An Outcome
A pencil bag holds 4 pens, 3 pencils, and 3 highlighters. What is the probability of picking out a pen from the bag without looking?
Probability involves part over whole. First, add up how many items are in the bag. There are 10 items. Then, count how many pens there are (4). Put 4 over 10 to get 
Example Question #23 : Probability
Ana put 5 black marbles, 3 blue marbles, and 2 green marbles into a bag. She then picked one marble out. What is the probability that the marble was black?
Given that there are 5 black marbles, 3 blue marbles, and 2 green marbles, there are a total of 10 marbles.
If Ana picks a marble, there are 5 marbles that are black. Thus, there would a 5 out of 10 chance that she would get a black marble.
We can convert to a percent by multiplying to get 100 in the denominator.
Fifty over one hundred is equal to 
Example Question #24 : Probability
There are 11 discs in a box, each one labeled with a number 1 through 11. Beth picks a disc out of the box. The first disc is the number 9. Beth is going to pick another disc. What is the likelihood that she will pick an odd disc next?
Initially the discs in the box were:
6 of these numbers are odd and 5 are even.
When Beth picked disc number 9, there remained 5 odd discs and 5 even discs.
Odd discs remaining:
There are ten total discs remaining. To find the probability of an odd disc:
This fraction is equal to one half, or 
Example Question #24 : How To Find The Probability Of An Outcome
Andrew has three quarters. If he flips the three quarters, what is the probability that the last quarter will be heads?
66 percent
50 percent
70 percent
33 percent
50 percent
When flipping a coin, the possibility that it will be heads or tails will always be 50/50. Even though Andrew flips the coin twice before the third flip, the prior flips do not affect the outcome of the third flip.
Example Question #25 : Probability
Molly baked a pie with 6 slices. 3 slices have a sugar topping, 1 slice has a fruit topping, and 2 slices have no topping. What percentage of the pie has a sugar topping?
The Molly baked a pie with 6 slices. 3 slices have a sugar topping, 1 slice has a fruit topping, and 2 slices have no topping. Therefore, the proportion of sugar slices to the rest of the pie is:
Given that 50% is the percent equivalent of 
Example Question #26 : Probability
In a turtle race, five turtles sprinted towards the finish line. Mary chose a turtle at random before the race. What is the chance that her turtle will finish in first or second place?
If there are 5 turtles racing, there is a 2 out of 5 chance that a certain turtle will be first or second place.
Convert this value to a decimal.
Convert the decimal to a percentage.
Example Question #23 : Data Analysis And Probability
Gregory is answering a multiple choice question that has 5 answer choices. He correctly eliminates 2 of the options, and then guesses. What chance does he have of answering the question correctly?
If there are 5 answer choices, and Gregory eliminates 2 of the answer choices, then there are 3 answer options left.
Of the 3 total options left, 1 of them is correct.
If he guesses, there is a 
Example Question #24 : Data Analysis And Probability
Jenny has 4 puppies that she is trying to get adopted. 3 of them have spots. One of the puppies is adopted, at random, from the group. What are the odds that the adopted puppy had spots?
To find the chance, we need to set up a fraction that looks like this:
Using the information from the question, we know that this fraction is equal to:
There is a 
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