Page 267 - Basic College Mathematics with Early Integers

244 C HAPTE R 3 I FRACTIONS

PRACTICE 2 Example 2 Multiply: 3 1 7
#
3 8
2 11
Multiply and simplify: 1 # Solution: 1
3 15 Recall from Section 3.6 that the mixed number 3 3 can be written as
10
the fraction . Then
3
1
# #
1 7 10 7 2 5 7 35 11
3 # = # = # # = or 2
3 8 3 8 3 2 4 12 12
1
Work Practice 2
Don’t forget that a whole number can be written as a fraction by writing the whole
number over 1. For example,
20 7
20 = and 7 =
1 1

3
PRACTICE 3 Example 3 Multiply: # 20
4
5
Multiply: # 18 1
6 3 3 20 3 20 3 4 5 15
#
# #
Solution: # 20 = # = = = or 15
#
#
4 4 1 4 1 4 1 1
1
Work Practice 3
When both numbers to be multiplied are mixed or whole numbers, it is a good idea
to estimate the product to see if your answer is reasonable. To do this, we first prac-
tice rounding mixed numbers to the nearest whole. If the fraction part of the mixed
1
number is or greater, we round the whole number part up. If the fraction part of
2 1
the mixed number is less than , then we do not round the whole number part up.
2
Study the table below for examples.

Mixed Number Rounding

~ is less than q.
1 1
5 Thus, 5 rounds to 5.
4 4
~ q
9 ; 9 is greater than 8 9
3 Thus, 3 rounds to 4.
16 : Half of 16 is 8. 16
1
3 ; 3 is less than 3 . 3
2
1 1 Thus, 1 rounds to 1.
7 : Half of 7 is 3 . 7
2
PRACTICE 4 Example 4 Multiply. Check by estimating.
Multiply. Check by estimating. 1
# #
#
1 3 2 1 5 9 5 9 5 3 3 15 3
3 # 2 Solution: 1 # 2 = # = = = or 3 Exact
#
#
5 4 3 4 3 4 3 4 3 4 4 4
1
Let’s check by estimating.
2 1 Copyright 2012 Pearson Education, Inc.
#
1 rounds to 2, 2 rounds to 2, and 2 2 = 4 Estimate
3 4
Answers
The estimate is close to the exact value, so our answer is reasonable.
2 4
2. 1 3. 15 4. 8 Work Practice 4
9 5