Name:
Date:
Mental Math and
Estimation
R
C
H A PTE
10
Lesson 1
Meaning of Sum
Find the sum of the numbers.
1.
512 and 350
+
5 1
3 5
2
0
350
512
?
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The sum of
2.
and
is
.
is
.
is
.
469 and 108
4
+ 1
108
469
6 9
0 8
?
The sum of
3.
and
275 and 354
+
2 7 5
3 5 4
354
275
?
The sum of
and
Extra Practice 2B
MS_Extra Practice_2B_Ch10_001-020.indd 1
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Name:
Date:
Solve.
Use bar models to help you.
4.
Julia saves $240.
Warrick saves $550.
Find the sum of money they save.
$550
$240
?
5.
.
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The sum of money they save is $
Alan writes two numbers.
One number is 529.
The other number is 360.
Find the sum of the two numbers.
529
360
?
The sum of the two numbers is
2
.
Chapter 10 Lesson 1
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Date:
Lesson 2
Mental Addition
Add mentally.
Fill in the blanks.
1.
24 + 3 =
2.
65 + 4 =
3.
87 + 2 =
4.
36 + 3 =
5.
54 + 5 =
6.
71 + 6 =
Find the missing numbers.
Add mentally.
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7.
35 + 6 = ?
35 +
=
6
–
=
4
.
So, 35 + 6 =
8.
10
67 + 5 = ?
=
67 +
–
So, 67 + 5 =
=
.
Extra Practice 2B
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Name:
Date:
9.
86 + 8 =
10.
26 + 9 =
11.
49 + 3 =
12.
58 + 4 =
Find the missing numbers.
Add mentally.
13.
236 + 2 = ?
6
236
=
6+
230
+
=
14.
473 + 2 =
15.
765 + 3 =
16.
267 + 1 =
17.
365 + 4 =
18.
549 + 7 = ?
7
10
=
549 +
3
–
So, 549 + 7 =
4
=
.
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.
So, 236 + 2 =
Chapter 10 Lesson 2
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19.
388 + 9 =
20.
454 + 7 =
21.
356 + 9 =
22.
157 + 3 =
Find the missing numbers.
Add mentally.
23.
425 + 30 = ?
20
425
+ 30 =
405
+
=
.
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So, 425 + 30 =
24.
716 + 50 =
25.
549 + 50 =
26.
657 + 40 =
27.
835 + 30 =
Find the missing numbers.
Add mentally.
28.
677 + 60 = ?
70
100
=
677 +
30
–
So, 677 + 60 =
=
.
Extra Practice 2B
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Name:
Date:
29.
351 + 70 =
30.
864 + 90 =
31.
786 + 80 =
32.
472 + 60 =
Fill in the missing numbers.
Add mentally.
33.
267 + 200 = ?
200
267
+ 200 =
67
+ 67 =
.
34.
351 + 200 =
35.
864 + 100 =
36.
408 + 500 =
37.
682 + 200 =
6
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So, 267 + 200 =
Chapter 10 Lesson 2
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Lesson 3
Meaning of Difference
Find the difference between the numbers.
1.
82
82 – 37
8 2
– 3 7
37
?
The difference between 82 and 37 is
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2.
650
650 – 420
6 5 0
– 4 2 0
420
?
The difference between 650 and 420 is
3.
.
.
900
900 – 575
9 0 0
– 5 7 5
575
?
The difference between 900 and 575 is
.
Extra Practice 2B
MS_Extra Practice_2B_Ch10_001-020.indd 7
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Name:
Date:
Solve.
Use bar models to help you.
4.
Sally sold 450 burgers.
Jenny sold 230 burgers.
Find the difference between the number of burgers they sold.
450
?
The difference is
5.
burgers.
Kaylene baked 150 muffins on Tuesday.
She baked 77 muffins on Thursday.
What is the difference between these two amounts?
150
77
?
The difference is
8
muffins.
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230
Chapter 10 Lesson 3
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Date:
Lesson 4
Mental Subtraction
Subtract mentally.
Fill in the blanks.
1.
29 – 2 =
2.
47 – 1 =
3.
65 – 4 =
4.
54 – 4 =
5.
79 – 7 =
6.
88 – 6 =
Find the missing numbers.
Subtract mentally.
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7.
53 – 9 = ?
9
10
– 10 =
1
+
So, 53 – 9 =
8.
=
.
74 – 6 = ?
– 10 =
+
So, 74 – 6 =
=
.
Extra Practice 2B
MS_Extra Practice_2B_Ch10_001-020.indd 9
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Name:
Date:
9.
61 – 7 =
10.
32 – 9 =
11.
42 – 8 =
12.
94 – 5 =
Find the missing numbers.
Subtract mentally.
13.
536 – 5 = ?
6
536
–5=
530
+
=
.
14.
688 – 4 =
15.
829 – 7 =
16.
529 – 1 =
17.
486 – 4 =
18.
473
–
5 ?=
5
10
=
473 –
5
+
So, 473 – 5 =
10
=
.
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So, 536 – 5 =
Chapter 10 Lesson 4
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Name:
Date:
19.
764 – 8 =
20.
821 – 9 =
21.
423 – 5 =
22.
651 – 7 =
Find the missing numbers.
Subtract mentally.
23.
492 – 30 = ?
90
492
– 30 =
402
+
=
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So, 492 – 30 =
.
24.
286 – 60 =
25.
763 – 50 =
26.
258 – 10 =
27.
657 – 40 =
Find the missing numbers.
Add mentally.
28.
361 – 70 = ?
70
100
– 100 =
30
+
So, 361 – 70 =
=
.
Extra Practice 2B
MS_Extra Practice_2B_Ch10_001-020.indd 11
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Name:
Date:
29.
530 – 90 =
30.
240 – 50 =
31.
560 – 80 =
32.
820 – 90 =
Find the missing numbers.
Subtract mentally.
33.
428 – 200 = ?
28
428
– 200 =
400
So, 428 – 200 =
=
.
34.
645 – 300 =
35.
831 – 600 =
36.
780 – 400 =
37.
905 – 700 =
12
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+
Chapter 10 Lesson 4
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Date:
Lesson 5
Rounding Numbers to Estimate
Mark each number with an ✗ on the number line.
Round each number to the nearest ten.
Circle it on the number line.
Then fill in the blanks.
16
10
1.
16 is nearer to
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16 is about
2.
23 is nearer to
23 is about
3.
32 is nearer to
32 is about
4.
44 is nearer to
44 is about
23
20
44
32
30
than to
40
50
.
when rounded to the nearest ten.
than to
.
when rounded to the nearest ten.
than to
.
when rounded to the nearest ten.
than to
.
when rounded to the nearest ten.
Extra Practice 2B
MS_Extra Practice_2B_Ch10_001-020.indd 13
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Name:
Date:
Look at the digits in the tens place.
Then fill in the blanks.
5.
78
78 is between
and
.
6.
91
91 is between
and
.
7.
458
458 is between
and
.
8.
853
853 is between
and
.
Number
Number line
Write using ‘is about’
9.
425
420
430
is about
.
10.
652
650
660
is about
.
11.
856
850
860
is about
.
14
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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.
Chapter 10 Lesson 5
MS_Extra Practice_2B_Ch10_001-020.indd 14
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Name:
Date:
Complete the table.
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Number
Rounded to the
nearest ten
Write using ’is about’
12.
98
is about
.
13.
125
is about
.
14.
369
is about
.
15.
424
is about
.
16.
652
is about
.
17.
856
is about
.
The numbers in each problem are rounded to the nearest ten.
Find the greatest and least number that was rounded.
Use the number line to help you.
18.
A camera costs about $50.
45
50
55
The greatest amount the camera could cost is $
The least amount the camera could cost is $
.
.
Extra Practice 2B
MS_Extra Practice_2B_Ch10_001-020.indd 15
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Name:
A swimming pool is about 80 meters long.
75
80
The greatest length the pool could be is
The least length the pool could be is
20.
meters.
meters.
The mass of a bag of rice is about 500 grams.
495
500
The greatest mass of the rice could be
The least mass of the rice could be
16
85
505
grams.
grams.
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19.
Date:
Chapter 10 Lesson 5
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Date:
Find the sum or difference.
Then round each number to the nearest ten.
Estimate the sum or difference to check that the answer
is reasonable.
21.
268 + 323 =
268 is about
.
323 is about
.
+
=
So, 268 + 323 is about
.
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Is the answer reasonable? Explain.
22.
479 – 124 =
479 is about
.
124 is about
.
–
So, 479 – 124 is about
=
.
Is the answer reasonable? Explain.
Extra Practice 2B
MS_Extra Practice_2B_Ch10_001-020.indd 17
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Name:
Date:
Find the sum or difference.
Then round each number to the nearest ten.
Estimate the sum or difference to check that the answer
is reasonable.
23.
235 + 552 =
Check:
+
=
Is the answer reasonable? Explain.
574 − 296 =
Check:
–
=
Is the answer reasonable? Explain.
18
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24.
Chapter 10 Lesson 5
MS_Extra Practice_2B_Ch10_001-020.indd 18
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Date:
Fill in the missing numbers or words.
25.
Daniel has $100 to buy these items.
Round the cost of each item to the nearest ten.
Then estimate the total cost.
A school bag costs $38.
when rounded to the nearest ten.
a. $38 is
A box of crayons costs $11.
when rounded to the nearest ten.
b. $11 is
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A pair of shoes costs $27.
c.
when rounded to the nearest ten.
$27 is
A textbook costs $18.
when rounded to the nearest ten.
d. $18 is
The estimated total cost is $
.
Does Daniel have enough money to pay for all the items?
.
Extra Practice 2B
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Name:
Date:
Put on Your Thinking Cap!
Juliana thinks of two numbers.
The sum of the two numbers is 20.
The difference between the two numbers is 6.
What are the numbers?
The numbers are
2.
and
Study the numbers in A.
Use the pattern in A to find the missing numbers in B.
28
13
4
?
15
9
20
6
A
The missing numbers are
20
.
12
?
8
16
B
and
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1.
.
Chapter 10 Put on Your Thinking Cap!
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