Page 57 - Probability Demystified

46 CHAPTER 3 The Addition Rules

PRACTICE

1. In a box there are 3 red pens, 5 blue pens, and 2 black pens. If a
person selects a pen at random, find the probability that the pen is

a. A blue or a red pen.
b. A red or a black pen.

2. A small automobile dealer has 4 Buicks, 7 Fords, 3 Chryslers, and
6 Chevrolets. If a car is selected at random, find the probability
that it is
a. A Buick or a Chevrolet.
b. A Chrysler or a Chevrolet.
3. In a model railroader club, 23 members model HO scale, 15 members
model N scale, 10 members model G scale, and 5 members model
O scale. If a member is selected at random, find the probability that
the member models
a. N or G scale.
b. HO or O scale.
4. A package of candy contains 8 red pieces, 6 white pieces, 2 blue
pieces, and 4 green pieces. If a piece is selected at random, find the
probability that it is
a. White or green.
b. Blue or red.
5. On a bookshelf in a classroom there are 6 mathematics books,
5 reading books, 4 science books, and 10 history books. If a student
selects a book at random, find the probability that the book is

a. A history book or a mathematics book.
b. A reading book or a science book.

ANSWERS
5 3 8 4
1. a. P(blue or red) ¼ P(blue) þ P(red) ¼ þ ¼ ¼
10 10 10 5

3 2 5 1
b. P(red or black) ¼ P(red) þ P(black) ¼ þ ¼ ¼
10 10 10 2