1. Warm Up
Problem of the Day
Lesson Presentation
Lesson Quizzes

2. Warm Up
Estimate by rounding to the nearest integer.
(–8.23)
– 3.16 8 –1 6 18

3. Problem of the Day
Complete the magic square. The sum of each row, column, and diagonal must be the same number.
0.5 7
4.625
8.75
6.375
5.25 4
2.25
2.875

4. Learn to add and subtract decimals.

5. One of the coolest summers on record in the Midwest was in 1992
One of the coolest summers on record in the Midwest was in The average summertime temperature that year was 66.8°F. Normally, the average temperature is 4°F higher than it was in 1992.
To find the normal average summertime temperature in the Midwest, you can add 66.8°F and 4°F.

6. 66.8 + 4.0 70.8 Use zero as a placeholder so that
both numbers have the same number
of digits after their decimal points.
70.8
Add each column just as you would
add integers.
Line up the decimal points.
The normal average summertime temperature in the Midwest is 70.8°F.

7. Additional Example 1A: Adding Decimals
Add. Estimate to check whether each answer is
is reasonable.
4.55
Line up the decimal points.
Use zero as a placeholder.
15.85
Add.
Estimate
= 16
15.85 is a reasonable answer.

8. Additional Example 1B: Adding Decimals
Add. Estimate to check whether each answer is
is reasonable.
6.44
Line up the decimal points.
Use zeros as placeholders.
22.44
Add.
Estimate
= 22
22.44 is a reasonable answer.

9. When adding numbers with the same sign, find the sum of their absolute values. Then use the sign of the numbers.
Remember!

10. Additional Example 1C: Adding Decimals
Add. Estimate to check whether each answer
is reasonable.
– (–10.972)
– (–10.972)
Think:
8.330
Line up the decimal points.
Use zero as a placeholder.
19.302
Add.
– (–10.972) = –19.302
Use the sign of the two
numbers.
Estimate
–8 + (–11) = –19
– is a reasonable
answer.

11. Check It Out: Example 1A
Add. Estimate to check whether each answer is
is reasonable.
6.78
Line up the decimal points.
Use zero as a placeholder.
19.98
Add.
Estimate
= 20
19.98 is a reasonable answer.

12. Check It Out: Example 1B
Add. Estimate to check whether each answer is
is reasonable.
4.21
Line up the decimal points.
Use zeros as placeholders.
38.21
Add.
Estimate
= 38
38.21 is a reasonable answer.

13. Check It Out: Example 1C
Add. Estimate to check whether each answer is
reasonable.
– (–13.852)
– (–13.852)
Think:
7.890
Line up the decimal points.
Use zero as a placeholder.
21.742
Add.
– (–13.852) = –21.742
Use the sign of the two
numbers.
Estimate
– is a reasonable
answer.
–8 + (–14) = –22

14. Additional Example 2: Subtracting Decimals
5.34
Line up the decimal points.
–2.08
3.26
Subtract.
B. 28 –
28.000
Use zeros as placeholders.
–15.911
Line up the decimal points.
12.089
Subtract.

15. Line up the decimal points. –1.46
Check It Out: Example 2
Subtract.
A – 1.46
3.57
Line up the decimal points.
–1.46
2.11
Subtract.
B. 34 –
34.000
Use zeros as placeholders.
–12.462
Line up the decimal points.
21.538
Subtract.

16. Additional Example 3: Application
During one month in the United States,
million commuter trips were taken on buses,
and million commuter trips were taken
on light rail. What was the total number of trips
taken on buses and light rail? Estimate to check
whether your answer is reasonable.
Use zero as a place holder.
Line up the decimal points.
Add.
Estimate
= 518
is a reasonable answer.
The total number of trips was million.

17. Check It Out: Example 3
In 1999, million bushels of corn were
grown in the United States. In 2000, the harvest
yielded million bushels. What was the
total production for those two years? Estimate
to check whether your answer is reasonable.
Use zero as a place holder.
Line up the decimal points.
Add.
Estimate
= 314
The total number of bushels was million.

18. Lesson Quizzes
Standard Lesson Quiz
Lesson Quiz for Student Response Systems

19. Lesson Quiz: Part I
Add. Estimate to check whether your answer is reasonable.
2. – (–19.2) 1.
21.25; Estimate: = 21
–27.66; Estimate: -8 + (-19) = -27
Subtract. Estimate to check whether your answer is reasonable.
6.72 – 4.16
4. 24 – 3.8 3.
2.56; Estimate: 7 – 4 = 3
20.2; Estimate: = 20

20. Lesson Quiz: Part II
Subtract. Estimate to check whether your answer is reasonable.
5. Renee finished her first lap in the 200 m freestyle
event in seconds. She completed the second lap in seconds. By how much did her time increase in the second lap? Estimate to check whether your answer is reasonable.
1.41 seconds; Estimate: 30 – 29 = 1

21. Lesson Quiz for Student Response Systems
1. Identify the sum and then estimate to check whether the answer is reasonable.
A ; estimate: = 20
B ; estimate: = 20
C ; estimate: = 19
D ; estimate: = 19

22. Lesson Quiz for Student Response Systems
2. Identify the sum and then estimate to check whether the answer is reasonable.
– (–18.1)
A. –8.78; estimate: –9 + (–18) = –9
B. –27.42; estimate: –9 + (–18) = –9
C. –27.42; estimate: –9 + (–18) = –27
D. –8.78; estimate: –9 + (–18) = –27

23. Lesson Quiz for Student Response Systems
3. Identify the difference and then estimate to check whether the answer is reasonable.
7.63 – 3.25
A. 4; estimate: 7 – 3 = 4
B. 4.22; estimate: 7 – 3 = 4
C. 4.32; estimate: 8 – 3 = 5
D. 4.38; estimate: 8 – 3 = 5

24. Lesson Quiz for Student Response Systems
4. Identify the difference and then estimate to check whether the answer is reasonable.
35 – 2.7
A. 32; estimate: 35 – 3 = 32
B. 32.3; estimate: 35 – 3 = 32
C. 33; estimate: 35 – 2 = 33
D. 33.3; estimate: 35 – 2 = 33

25. Lesson Quiz for Student Response Systems
5. Margaret took an exam that has two parts. She completed the first part in minutes and the second part in minutes. By how much did her time increase in the second part? Estimate to check whether the answer is reasonable.
A. 16 min; estimate: 33 – 17 = 16
B min; estimate: 32 – 17 = 15
C min; estimate: 32 – 18 = 14
D. 10 min; estimate: 30 – 20 = 10