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1 Lesson 1 Meaning of Sum

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1

CHAPTER

10

Name: Date:

Mental Math and Estimation

Practice 1 Meaning of SumFind the sum of the numbers.

96 and 73

The sum of 96 and 73 is .

9 6+ 7 3

Example

1. 700 and 200

7 0 0+ 2 0 0

700

?

200

The sum of and is .

2. 215 and 507

2 1 5+ 5 0 7

215

?

507

The sum of and is .

96

?

73

04(M)MIF2015CC_WBG2B_Ch10.indd 1 29/04/13 3:37 PM

Chapter 10 Mental Math and Estimation2

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Solve.Use bar models to help you.

3. Al spent $27 on a shirt and $120 on books. Find the sum of money Al spent.

+ =

The sum of money Al spent is $ .

4. Harry is 12 years old. His sister is 9 years younger. Find the sum of their ages.

+ =

The sum of their ages is years.

5. Greg has collected 32 green jumping beans. His mother gives him 15 red jumping beans more. Find the sum of jumping beans Greg has now.

+ =

The sum of jumping beans Greg has now is .

– =


3 Lesson 2 Mental Addition

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Climb each step by adding mentally.

1.

21 + 873 + 3

45 + 454 + 3

96 + 272 + 7

63 + 493 + 6

Find the missing numbers. Add mentally.

2. 75 + 6 = ?

10

6

75 + =

– =

So, 75 + 6 = .

3. 69 + 5 = 4. 48 + 4 =

5. 29 + 9 = 6. 65 + 8 =

Practice 2 Mental Addition

Name: Date:

Example38 + 7 = ?

10

7

38 + =

– =

So, 38 + 7 = .



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Find the missing numbers.Add mentally.

7. 632 + 7 =

8. 712 + 3 =

9. 534 + 5 =

Example123 + 5 = ?

123

120

+ 5 =

+ =

So, 123 + 5 = .

Example409 + 7 = ?

10

7

409 + =

– =

So, 409 + 7 = .

10. 375 + 6 =

11. 275 + 8 =

12. 629 + 9 =


5 Lesson 2 Mental Addition

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13. 348 + 50 =

14. 741 + 30 =

15. 653 + 10 =

246 + 20 = ?

246

206

+ 20 =

+ =

So, 246 + 20 = .

Example

16. 427 + 80 =

17. 535 + 90 =

18. 164 + 60 =

352 + 70 = ?

100

70

352 + =

– =

So, 352 + 70 = .

Example

Name: Date:




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19. 765 + 100 = ?

765

65

+ 100 =

+ =

So, 765 + 100 = .

Add mentally.

20. 452 + 500 =

21. 264 + 300 =

22. 412 + 300 =

23. 178 + 300 =

24. 708 + 200 =

25. 320 + 600 =

Example315 + 200 = ?

315

15

+ 200 =

+ =

So, 315 + 200 = .



7 Lesson 3 Meaning of Difference

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40

17

Name: Date:

Practice 3 Meaning of Difference Find the difference between the numbers.

Example

40 and 17

4 0– 1 7

– =

The difference between 40 and 17 is .

1. 156 and 82

1 5 6– 8 2

156

82 – =


2. 800 and 785

8 0 0– 7 8 5

800

785 – =




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3. Tonya collected 320 friendship bracelets and her sister collected 290. Find the difference between the number of friendship bracelets.

320

290

Tonya

Sister

?

– =

The difference is friendship bracelets.

4. Joe and Susan went for a run. Joe ran 24 laps and Susan ran 15 laps. Find the difference between the number of laps they ran.

24 laps

15 laps ?

Joe

Susan

– =

The difference is laps.


9 Lesson 3 Meaning of Difference

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Name: Date:


5. Kiki baked 120 muffins on Monday. She baked 219 muffins on Tuesday. What is the difference between these two amounts?

120 muffins

219 muffins

?

Monday

Tuesday

– =

The difference is muffins.

6. Mr. Wong wants to buy a camera that costs $401. He saved $315. What is the difference between the amounts of money?

$401

$315 ?

Camera

Savings

– =

The difference is $ .

The difference shows how much more money Mr. Wong needs to buy the camera.



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7. Elizabeth has a blue ribbon and a red ribbon. The blue ribbon is 27 centimeters long. The red ribbon is 18 centimeters long. What is the difference between their lengths?

Blue ribbon

Red ribbon

?

27 cm

18 cm

– =

The difference is centimeters.


11 Lesson 4 Mental Subtraction

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Practice 4 Mental Subtraction

Name: Date:

Find the missing numbers. Subtract mentally.

1. 56 − 8 = ?

10

8

56 − =

+ =

So, 56 − 8 = .

Subtract mentally.

2. 84 − 7 =

3. 38 − 9 =

4. 62 − 8 =

5. 76 − 7 =

Example43 − 6 = ?

10

6

43 − =

+ =

So, 43 − 6 = .



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Example

789 − 5 � ?

789

780

− 5 =

+ =

So, 789 − 5 = .

6. 398 − 4 =

7. 427 − 2 =

8. 358 − 6 =


Example

364 − 6 = ?

10

4

364 − =

+ =

So, 364 − 6 = .

9. 472 − 3 =

10. 513 − 9 =

11. 394 − 7 =


13 Lesson 4 Mental Subtraction

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Name: Date:


Example

348 − 20 � ?

348

308

− 20 =

+ =

So, 348 − 20 = .

12. 475 − 40 =

13. 466 − 30 =

14. 654 − 50 =


Example

641 − 50 = ?

100

50

641 − =

+ =

So, 641 − 50 = .

15. 516 − 70 =

16. 228 − 30 =

17. 436 − 40 =



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19. 348 − 300 =

20. 548 − 300 =

21. 615 − 400 =

22. 465 − 200 =

Example256 − 100 = ?

256

56

− 100 =

+ =

So, 256 − 100 = .

18. 832 − 400 = ?

832

32

− 400 =

+ =

So, 832 − 400 = .


15 Lesson 5 Rounding Numbers to Estimate

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Name: Date:

Example

12 is nearer to than to .

12 is about when rounded to the nearest ten.

1. 48 is nearer to than to .


2. 35 is about when rounded to the nearest ten.

3. 26 is nearer to than to .


20

...

10

Practice 5 Rounding Numbers to Estimate Mark each number with an ✗ on the number line.

48 35 26

10 20 30 40 50 60

Round each number to the nearest ten. Circle it on the number line. Then fill in the blanks.



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Example

37 is between and .

4. 86 86 is between and .




Mark each number with an ✗ on the number line. Round each number to the nearest ten. Circle the number on the number line. Then fill in the last column of the table.

Look at the digits in the tens place. Then fill in the blanks.

Number Number line Write using 'is about'

Example315 310 315 320 is about

769760

501510

896890

8.

9.

10.900

500

770

04(M)MIF2015CC_WBG2B_Ch10.indd 16 4/30/13 3:19 AM


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Complete the table.

NumberRounded to the

nearest tenWrite using 'is about'

Example78

is about

15

34

217

697

728

11.

12.

13.

14.

15.

The numbers in each problem are rounded to the nearest ten. Find the greatest and least number that is rounded.Use the number line to help you.

Example

Mr. Johnson spent about $80 at a department store.

75 80 8570

The greatest amount he could have spent is $ .

The least amount he could have spent is $ .

Name: Date:



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16. Charles drinks about 790 milliliters of fruit juice in one day.

785 790 795780

The greatest amount he could have had is milliliters.

The least amount he could have had is milliliters.

17. Shateel ran about 750 meters.

745 750 755740

The greatest distance she could have run is meters.

The least distance she could have run is meters.

18. The mass of a bag of potatoes is about 830 grams.

825 830 835820

The greatest mass of the potatoes could be grams.

The least mass of the potatoes could be grams.



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Find the sum or difference. Then round each number to the nearest ten. Estimate the sum or difference to check that the answers are reasonable.

Example

763 + 36 = 799

763 is about .

36 is about .

760 + 40 = .

So, 763 + 36 is about .

Is the answer reasonable?

Explain.

19. 238 + 98 =

238 is about .

98 is about .

+ = .

So, 238 + 98 is about .

Is the answer reasonable? Explain.

20. 847 – 95 =

847 is about .

95 is about .

– = .

So, 846 – 95 is about .


Name: Date:



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21. 781 + 49 =

Check: + = .


22. 259 – 72 =

Check: – = .


23. The school principal has $900 to buy items for the school. Round the cost of each item to the nearest ten. Then estimate the total cost.

A set of 4 textbooks costs $96.

a. 96 is when rounded to the nearest ten.

A printer costs $215.

b. 215 is when rounded to the nearest ten.

A camera costs $147.

c. 147 is when rounded to the nearest ten.

A computer costs $385.

d. 385 is when rounded to the nearest ten.

The estimated total cost is $ .

Does the principal have enough money to pay for all the items?


21Chapter 10 Mental Math and Estimation

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VocabularyFill in the blanks with words from the box.

1. You can use an estimate to check that a sum

is .

2. 86 is 90 when rounded to the .

3. Add to find the of two or more numbers.

4. Subtract to find the between two or more numbers.

Concepts and SkillsAdd mentally.

5. 325 + 9 = 6. 436 + 20 =

7. 691 + 70 = 8. 635 + 300 =

Subtract mentally.

9. 541 – 5 = 10. 863 – 50 =

11. 238 – 70 = 12. 617 – 400 =

Round each number to the nearest ten.

13. 65 is about . 14. 132 is about .

15. 29 is about . 16. 396 is about .

Chapter Review/Test

Name: Date:

sum

difference

nearest ten

reasonable



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Find the sum or difference. Then round each number to the nearest ten to check that the answers are reasonable.

17. 76 + 83 = 18. 182 + 95 =

+ = + =

19. 628 – 145 = 20. 598 – 136 =

− = − =

Problem SolvingSolve. Then use estimation to check that the answers are reasonable.21. Mrs. Brown buys a set of books and a giant teddy bear. The set of books costs $154. The giant teddy bear costs $122. Find the sum of the amount for both prices.

+ =

Check: + = . Is the answer reasonable? Explain.

The two things cost about $ .

22. Pete earns $103 a month delivering newspapers. Shawn earns $175 a month delivering pizzas. What is the difference in the amounts they earn?

− =

Check: − = . Is the answer reasonable? Explain.

The difference is about $ .


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