Page 269 - Basic College Mathematics with Early Integers

246 C HAPTE R 3 I FRACTIONS

When adding or subtracting mixed numbers and whole numbers, it is a good idea
to estimate to see if your answer is reasonable.

For the rest of this section, we leave most of the checking by estimating to you.

4 4
PRACTICE 10 Example 10 Add: 3 + 1
5 15
5 6
Add: 3 + 2 Solution: The LCD of the denominators 5 and 15 is 15.
14 7
4 12
3 = 3
5 15
4 4
+ 1 = 1
15 15 Add the fractions; then add the whole numbers.
16
4 Notice that the fraction part is improper.
15
16 1
Since is 1 , we can write the sum as
15 15
16 1 1
4 =4+1 =5
15 15 15

Work Practice 10

Concept Check Explain how you could estimate the following sum:
1 10
5 + 14 .
9 11
4 1
PRACTICE 11 Example 11 Add: 2 + 5 + 1
5 2
6 1
Add: 12 + 3 + 2 Solution: The LCD of the denominators 5 and 2 is 10.
7 5
4 8
2 = 2
5 10
5 = 5
1 5
+ 1 = 1
2 10
13 3 3
8 = 8 + 1 = 9
PRACTICE 12 10 10 10
7 5 Work Practice 11
Subtract: 32 - 16 . Check
9 18
by estimating. Example 12 Subtract: 8 3 - 5 2 . Check by estimating.
7 21
Answers Solution: The LCD of the denominators 7 and 21 is 21.
3 2 1
10. 6 11. 18 12. 16 3 9
14 35 2 8 = 8 ; The LCD of 7 and 21 is 21.
7 21
2 2
Concept Check Answer - 5 =- 5
Round each mixed number to the 21 21 Copyright 2012 Pearson Education, Inc.
1
nearest whole number and add. 5 7
9 3 ; Subtract the fractions.
10 21
rounds to 5 and 14 rounds to 15, and
11 c
the estimated sum is 5 + 15 = 20 . Subtract the whole numbers.