To review these concepts, go to The Basics of Probability Study Guide.
The Basics of Probability Practice Questions
Practice
A box contains 50 balls that are alike in all ways except that 5 are white, 10 are red, 15 are blue, and 20 are green. The box has been shaken up, and one ball will be drawn out blindly.
 What color is most likely to be drawn?
 What color is least likely to be drawn?

Find the probability that the following will be drawn out:
a. a white ball
b. a red ball
c. a blue ball
d. a green ball
e. a yellow ball
f. a blue or green ball
g. a red, white, or blue ball
h. a ball that isn't green
Practice
A deck of ten cards contains one card with each number:

One card is selected from the deck. Find the probability of selecting each of the following:
a. an odd number
b. an even number
c. a number less than 5
d. a number greater than 5
e. a 5
f. a number less than 5, greater than 5, or equal to 5
g. a number less than 10
h. a multiple of 3
 A card will be randomly drawn and then returned to the deck. Then another card will be randomly drawn (possibly the first card again), and the two resulting numbers will be added together. Find the probability that their sum will be one of the following. [Hint: Make a table showing the first and second cards selected, similar to the dice table used for the sample questions.]
a. a sum of 2
b. a sum of 3
c. a sum of 21
d. a sum of 2 or 3
e. a sum of more than 3
f. a sum of less than 20

One card is selected from the deck and put back in the deck. A second card is then selected.
a. What is the most likely sum to be selected? What is its probability?
b. What is the least likely sum to be selected? What is its probability?
Practice
These word problems illustrate some practical examples of probability in everyday life. They also show you some of the ways your knowledge of probability might be tested on an exam.

A bag of jelly beans has 10 yellow, 19 purple, 24 blue, 17 pink, 29 red, and 21 green jelly beans. What's the probability that when Ben picks a jelly bean out of the bag, it will be either purple or green?
a. 0.175
b. 0.475
c. 0.158
d. 0.333
e. 0.28

If you randomly select a month out of the year, what will the probability be that it will begin with the letter "J"?
a.
b.
c.
d.
e. 3

Lindsay and Jordan have teamed up to do an oral Spanish test together. If Lindsay knows there is chance that she'll draw a word that she knows, and Jordan knows that there is a chance that he'll draw a word that he knows, what is the probability that a single word will be known by either Lindsay or Jordan if there are 24 words in total on the oral exam?
a.
b.
c.
d.
e. cannot be determined with the given information

If two dice are rolled, what is the probability that the outcome will be doubles?
a.
b.
c.
d.
e.

There are an equal number of boys and girls in Ms. Laimon's kindergarten class. If two students are selected at random to carry the class banner in the Memorial Day Parade, what is the probability that they are both girls?
a.
b.
c.
d.
e. cannot be determined from the data given
Solutions
 green
 white

a.
b.
c.
d.
e. 0
f.
g.
h.

a.
b.
c.
d.
e.
f.
g.
h.

a.
b.
c. 0
d.
e.
f.

a. 11, with a probability of , or 0.1
b. 2 and 20, each with a probability of , or 0.01
 d.
 c.
 e.
 b.
 d.
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