Basic Mathematics for College Students

4.2 Adding and Subtracting Decimals 339

SolveTo evaluate , we work from left to right and perform the
subtraction first, then the addition.
9

Next, we add the 4.9-pound gain to the previous result to find the player’s weight
after two weeks of practice.

StateThe player’s weight was 339.2 pounds after two weeks of practice.

CheckWe can estimate to check the result. The player lost about 16 pounds the
first week and then gained back about 5 pounds the second week, for a net loss of
11 pounds. If we subtract the approximate 11 pound loss from his beginning weight,
we get 350  11  339 pounds. The result, 339.2 pounds, seems reasonable.

334

1

.3

 4.9

339.2

Write the whole number 350 as 350.0 and use a two-column

borrowing process to subtract in the tenths column.

This is the player’s weight after one week of practice.

35

4

0

10

.0

10

 15.7

334.3

350 15.74.9

1.148.058 2.155.4 3.2.578 4.7.36 5.4.65 6.4.06 7.1.84 8.9.3

9. a. 810 b. 460 10.$209.90 11.0.0255 in. 12.192.7 lb

ANSWERS TO SELF CHECKS

SECTION 4.2 STUDY SET

VOCABULARY

Fill in the blanks.

1. In the addition problem shown below, label each
   addendand the sum.


2. When using the vertical form to add decimals, if the
   addition of the digits in any one column produces a
   sum greater than 9, we must.


3. In the subtraction problem shown below, label the
   minuend, subtrahend,and the difference.


4. If the subtraction of the digits in any place-value
   column requires that we subtract a larger digit from
   a smaller digit, we must or regroup.


5. To see whether the result of an addition is reasonable,
   we can round the addends and the sum.

12.9

 4.3

8.6

1.72

4.68

 2.02

8.42

6. In application problems, phrases such as how much
   older, how much longer,and how much thicker
   indicate the operation of.

CONCEPTS

7. Check the following result. Use addition to determine
   if 15.2 is the correct difference.


8. Determine whether the signof each result is positive
   or negative.You do not have to find the sum.
   a.
   b.
   c.


9. Fill in the blank: To subtract signed decimals, add the
   of the decimal that is being subtracted.


10. Apply the rule for subtraction and fill in the three
    blanks.

3.6(2.1)3.6 

133.2(400.43)

24.9929.08

7.6(1.8)

28.7

 12.5

15.2