Finding Sums and Differences with Mental Math

Topic 2 Reteaching

Adding and Subtracting Decimals to the Hundredths

Reteach Pages- 103 + 104

Poll

Look over pages 103 + 104. We will use these pages as our study guide. How do you feel about adding and subtracting decimals?

• GREAT! I am ready for the test!

• OK....but I might need a little review before the test.

• Not so grreat....I've got some questions for you.

Set A

Use mental math to add and subtract decimals

Set A: Use Mental Math to add and subtract decimals

• Remember: you do not need to use mental math. You can use the standard algorithm. Answer each question on your paper.

• Be ready to play in 5 minutes

Multiple Choice

8.6 + 23.4 + 1.4=

• 34.0

• 33.4

• 334

• 33.0

Multiple Choice

27 - 9.9=

• 12

• 7.2

• 12.1

• 17.1

Multiple Choice

13.5 + 5.7 + 36.5=

• 55.7

• 55

• 5.57

• 35

Multiple Choice

205.4 - 99.7=

• 105.4

• 105.7

• 10.54

• 10.57

Poll

How did you do with Set A?

• Great! I got all 4 correct.

• Pretty good. I only got 1 wrong but I understand my mistake.

• OK. I got 2-3 wrong but I understand my mistakes.

• I have questions. I got 1 - 4 wrong and I don't understand my mistakes.

Set B:

Use compatible numbers to estimate sums and differences.

Set B: Use compatible numbers to estimate sums and differences

• Answer questions 1 -4 in your book.

• Be ready to play in 4 minutes.

Multiple Choice

Estimate the sum: 358 + 293

• 200

• 700

• 100

• 6,000

Multiple Choice

Estimate the difference: 15.01 - 4.4=

• 11.1

• 1.1

• 10

• 5

Multiple Choice

Estimate the sum: 80.01 + 2.89=

• 85

• 7.5

• 70

• 100

Multiple Choice

Estimate the difference: 25,003 - 12,900=

• 12,000

• 1,300

• 27,000

• 28,000

Poll

How did you do with Set B?

• Great! I got all 4 correct!

• Pretty good. I only got 1 wrong but I understand my mistake.

• OK. I got 2 - 3 wrong but I understand my mistakes.

• I have questions. I got 1 - 4 wrong and I don't understand my mistakes.

Set C

Use models to find sums and differences of decimals

Set C: Using Models

• Answer questions 1 - 4 in set C.

• Be ready to play in 4 minutes.

Multiple Choice

Use the model to find the sum.

• 1.00

• 1.09

• 0.91

• 91

Multiple Choice

Use the model to find the difference.

• 0.98

• 0.67

• 0.46

• 0.36

Multiple Choice

Use the model to find the sum.

• 0.68

• 0.78

• 6.8

• 7.8

Multiple Choice

Use the model to find the difference.

• 0.81

• 1.59

• 0.3

• 0.03

Poll

How did you do with Set C?

• Great! I got all 4 correct.

• Good. I got 1 wrong but I understand my mistake.

• OK. I got a few wrong but I understand my mistakes.

• I have questions. I got 1 - 4 wrong and I don't understand my mistakes.

Set D:

Add and Subtract Decimals

Set D: Add and Subtract Decimals

• Remember to annex zeros as needed. Use your math notebook or whiteboard to solve if you need more space.

• Be ready to play in 7 minutes

Multiple Choice

7.06 + 0.85=

• 6.21

• 7.91

• 7.81

• 6.51

Multiple Choice

24.07 - 5.316=

• 29.09

• 31.11

• 16.354

• 18.754

Multiple Choice

51.92 - 28.003=

• 23.917

• 22.811

• 30.028

• 32.911

Multiple Choice

8.71 - 0.4=

• 9.11

• 8.67

• 8.31

• 9.72

Multiple Choice

98 + 3.79=

• 135.9

• 138.2

• 102.58

• 101.79

Multiple Choice

Talia measured two strings. The green string was 2.37 cm long. The blue string was 4 cm long. How many centimeters longer was the blue string than the green string?

• 6.37 centimeters

• 2.41 centimeters

• 1.63 centimeters

• 2.37 centimeters

Poll

How did your do with Set D?

• GREAT! I got all 6 correct.

• Good! I got 1 or 2 wrong but I understand my mistakes.

• OK. I got 3 or 4 wrong but I understand my mistakes.

• I have some questions. I got 5 or 6 wrong and I don't understand my mistakes.

Poll

Look over your paper from class today and the corrections you made.

How do you feel about Topic 2: Add and Subtract Decimals to the Hundredths?

• Great! I am ready for the test!

• OK. But I need some more review and practice before the test.

• Not so great.... I've got some questions for you.