Date:
P
H A TE
R
C
Name:
2
Mental Math and Estimation
Worksheet 1
Mental Addition
Add. Use mental math.
1.
35 ⫹ 4 ⫽
2.
43 ⫹ 6 ⫽
3.
20 ⫹ 50 ⫽
4.
30 ⫹ 60 ⫽
Complete each number bond.
6.
5.
30
100
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70
40
7.
8.
48
50
67
70
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Add mentally. First add the tens. Then add the ones.
Use number bonds to help you.
Example
42 ⫹ 35
72
42 ⫹ 35 ⫽
72
⫽
77
30
⫹5
35
5
36 ⫹ 53
50
36 ⫹ 50 ⫽
36 ⫹ 53 ⫽
⫹3
53
⫽
10.
57 ⫹ 22
20
57 ⫹ 20 ⫽
57 ⫹ 22 ⫽
⫽
18
⫹2
22
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9.
42 ⫹ 30 ⫽
Chapter 2 Lesson 2.1
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Fill in each missing number.
Example
37 40 3
11.
58 60 12.
69 1
13.
87 3
Add mentally. First add the tens. Then subtract the extra ones.
Use number bonds to help you.
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Example
45 28 75 14.
2
73
53 39 93 15.
34 47 84 16.
62 18 82 Reteach 3A
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Fill in the missing numbers.
Example
36 39 76
1
17.
47 27 3
18.
58 38 2
19.
54 26 4
20.
45 48 21.
56 27 22.
33 49 23.
24 46 24.
78 18 25.
47 39 20
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Add. Use mental math.
Chapter 2 Lesson 2.1
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Worksheet 2
Mental Subtraction
Complete each number bond.
1.
2.
52
64
4
2
Fill in the blanks. Then complete each number bond.
Example
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48
48 ⫽
4
tens
8
ones
40
3.
87 ⫽
tens
8
ones
87
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4.
23 ⫽
tens
ones
5.
98 ⫽
tens
ones
6.
51 ⫽
tens
one
Subtract.
7.
78 ⫺ 4 ⫽
8.
56 ⫺ 3 ⫽
9.
69 ⫺ 5 ⫽
10.
97 ⫺ 4 ⫽
22
23
98
51
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Chapter 2 Lesson 2.2
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Subtract mentally. First subtract the tens. Then subtract the ones.
Example
65 23 Step 1
11.
Step 2
5 ones 3 ones 2 ones
Step 3
65 23 tens tens tens
Step 2
ones ones ones
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87 34 68 43 Step 1
tens tens tens
Step 2
ones ones ones
Step 3
13.
42
87 34 Step 1
Step 3
12.
6 tens 2 tens 4 tens
68 43 89 54 Step 1
tens tens tens
Step 2
ones ones ones
Step 3
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Subtract. Use mental math.
14.
76 ⫺ 42 ⫽
15.
58 ⫺ 34 ⫽
16.
67 ⫺ 35 ⫽
17.
79 ⫺ 45 ⫽
Fill in the blanks.
2
.
18.
Subtracting 67 is the same as subtracting 70, then adding
.
19.
Subtracting 59 is the same as subtracting 60, then adding
.
20.
Subtracting 76 is the same as subtracting 80, then adding
.
Fill in the blanks.
Example
Subtracting 47 is the same as subtracting
50
, then adding 3.
21.
Subtracting 78 is the same as subtracting
, then adding 2.
22.
Subtracting 59 is the same as subtracting
, then adding 1.
23.
Subtracting 86 is the same as subtracting
, then adding 4.
24
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Example
Subtracting 48 is the same as subtracting 50, then adding
Chapter 2 Lesson 2.2
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Subtract.
24.
62 50 25.
74 40 26.
83 60 27.
91 30 Complete.
Example
73 30
73 28 43
45
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28.
2
62 40
62 37 3
29.
84 60
84 59 1
30.
91 60
91 56 4
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Fill in the missing numbers.
Example
31.
73 26 43
47
85 49 4
1
32.
64 38 2
92 57 3
34.
94 68 2
Subtract. Use mental math.
35.
73 27 36.
65 39 37.
81 58 38.
93 66 26
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33.
Chapter 2 Lesson 2.2
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Worksheet 3
More Mental Addition
Fill in the blanks.
Example
Adding 97 is the same as adding 100, then subtracting
3
.
1.
Adding 98 is the same as adding 100, then subtracting
.
2.
Adding 99 is the same as adding 100, then subtracting
.
3.
Adding 96 is the same as adding 100, then subtracting
.
Fill in the blanks.
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Example
100
Adding 96 is same as adding
, then subtracting 4.
4.
Adding 98 is the same as adding
, then subtracting 2.
5.
Adding 99 is the same as adding
, then subtracting 1.
6.
Adding 76 is the same as adding
, then subtracting 4.
Subtract. Use mental math.
7.
176 ⫺ 2 ⫽
8.
187 ⫺ 5 ⫽
9.
198 ⫺ 3 ⫽
10.
247 ⫺ 4 ⫽
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Complete.
Example
11.
73 100
64 100
73 98 64 97 164 3
161
52 100
52 99 13.
48 100
48 96 1
4
Complete.
Example
15.
14.
53 97 153
150
94 98 28
3
2
76 96 4
16.
95 99 1
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12.
2
Chapter 2 Lesson 2.3
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Complete.
Example
100 100
96 97 200
193
4
3
97
96
100
100
3
4
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100 100
17.
98 96 98
100
96
100
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100 100
18.
95 99 95
99
100
100
100 100
19.
98 94 98
100
94
100
Add mentally.
20.
63 98 21.
97 65 22.
99 76 23.
95 96 24.
96 97 25.
99 98 26.
97 97 27.
99 99 30
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Chapter 2 Lesson 2.3
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Worksheet 4
Rounding Numbers to Estimate
Complete.
Example
63
60
70
63 is nearer to
63 is
60
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1.
60
than to 70
.
when rounded to the nearest ten.
75
70
80
75 is exactly halfway between 70 and 80.
75 is
when rounded to the nearest ten.
2.
470
400
470 is nearer to
470 is
500
than to
.
when rounded to the nearest hundred.
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3.
725
700
800
725 is nearer to
725 is
than to
.
when rounded to the nearest hundred.
Round each number to the nearest ten and then to the nearest
hundred.
85
4.
79
5.
217
6.
791
7.
1,768
8.
9,809
32
Rounded to the
nearest ten
Rounded to the
nearest hundred
90
100
Rounded to the
nearest ten
Rounded to the
nearest hundred
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Example
Chapter 2 Lesson 2.4
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Mark the least number that rounds to the circled number with an X.
Mark the greatest number that rounds to the circled number with an X.
Example
the greatest number
that rounds to 40
the least number
that rounds to 40
30
50
40
List all the whole numbers that round to 40.
35 36 37 38 39 41 42 43 44
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9.
50
70
60
List all the whole numbers that round to 60.
10.
80
100
90
List all the whole numbers that round to 90.
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Mark the least number that rounds to the circled number with an X.
Mark the greatest number that rounds to the circled number with an X.
Example
the greatest number
that rounds to 500
the least number
that rounds to 500
400
500
600
600
700
800
700
800
900
800
900
1,000
12.
13.
34
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11.
Chapter 2 Lesson 2.4
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Find the sum. Then round to the nearest ten to check that your answer
is reasonable.
Example
78 27 105
78 is about 80.
27 is about 30.
80 30 110
105 is close to 110, so the answer is
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14.
64 73 64 is about
.
73 is about
.
15.
.
75 93 75 is about
.
93 is about
.
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Find the sum. Then round to the nearest hundred to check that your
answer is reasonable.
Example
267 451 718
267 451 is about 300 500 800
.
718 is close to 800, so the answer is reasonable.
553 292 553 292 is about
17.
.
.
.
.
118 293 118 293 is about
36
584 329 584 329 is about
20.
.
336 119 336 119 is about
19.
346 128 346 128 is about
18.
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16.
Chapter 2 Lesson 2.4
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Find the difference. Then round to check that your answer is
reasonable.
Example
82 37 45
82 37 is about 80 40 40
.
45 is close to 40, so the answer is reasonable.
21.
75 43 75 43 is about
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22.
.
.
.
.
674 492 674 492 is about
24.
438 249 438 249 is about
23.
918 374 918 374 is about
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25.
428 ⫹ 239 ⫽
26.
714 ⫹ 327 ⫽
27.
459 ⫺ 318 ⫽
28.
725 ⫺ 468 ⫽
38
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Find each sum or difference. Then round to the nearest ten to check
that your answer is reasonable.
Chapter 2 Lesson 2.4
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Worksheet 5
Using Front-End Estimation
Find the sum or the difference.
Then use front-end estimation to check that your answer
is reasonable.
Example
217 486 703
217 486 is about
200
400
600
.
The answer 703 is reasonable.
1.
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614 283 is about
2.
.
.
.
.
937 489 937 489 is about
4.
713 398 713 398 is about
3.
184 462 184 462 is about
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327 968 327 968 is about
6.
.
.
.
693 194 693 194 is about
40
.
908 702 908 702 is about
8.
694 294 694 294 is about
7.
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5.
Date:
Chapter 2 Lesson 2.5
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