rounding-value for grade 7 students_.ppt

rounding-off decimals

1. © T Madas

2. © T Madas
Sometimes we have to round numbers
What does rounding mean?
Can you think of
some examples?

3. © T Madas
4040
Rounding to the nearest
10
The rounded number must have a zero at the end
Round 37 to the nearest 10
30 37

4. © T Madas
Rounding to the nearest
10
The rounded number must have a zero at the end
Round 154 to the nearest 10
160150 154150

5. © T Madas
Rounding to the nearest
10
Round 125 to the nearest 10
130120 125 130
When our number lies halfway between “tens”,
we have agreed to round the number up.

6. © T Madas
Rounding to the nearest
10
Numbers ending in 1, 2, 3 and 4
get rounded down
Numbers ending in 5, 6, 7 , 8 and
9 get rounded up
Examples:
27 30
94 90
146 150
305 310
68 70
132 130
565 570
481 480

7. © T Madas
800800
Rounding to the nearest
100
The rounded number must have 2 zeros at the end
Round 764 to the nearest 100
700
764

8. © T Madas
12001200
The rounded number must have 2 zeros at the end
Round 1235 to the nearest 100
1300
1235
Rounding to the nearest
100

9. © T Madas
900900
Round 850 to the nearest 100
800 850
When our number lies halfway between
“hundreds”, we have agreed to round the
number up.
Rounding to the nearest
100

10. © T Madas
Numbers ending in 0s, 10s, 20s, 30s and 40s
get rounded down
Numbers ending in 50s, 60s, 70s , 80s and
90s get rounded up
Examples:
237 200
874 900
536 500
350 400
1168 1200
2032 2000
5750 5800
40081 40100
Rounding to the nearest
100

11. © T Madas
80008000
Rounding to the nearest
1000
The rounded number must have 3 zeros at the end
Round 7761 to the nearest 1000
7000
7761

12. © T Madas
80008000
The rounded number must have 3 zeros at the end
Round 8339 to the nearest 1000
9000
8339
Rounding to the nearest
1000

13. © T Madas
70007000
Round 6500 to the nearest 1000
6000 6500
When our number lies halfway between
“thousands”, we have agreed to round the number
up.
Rounding to the nearest
1000

14. © T Madas
Numbers ending in 00s, 100s, 200s, 300s and 400s
get rounded down
Numbers ending in 500s, 600s, 700s , 800s and
900s get rounded up
Examples:
2837 3000
4874 5000
5376 5000
7500 8000
1868 2000
2499 2000
29780 30000
45681 46000
Rounding to the nearest
1000

15. © T Madas
Practice Rounding
to the nearest…

16. © T Madas
Round these numbers to the nearest…
48
87
184
145
1563
3217
2005
50
90
180
150
1560
3220
2010
…10
209
2867
3467
1095
1550
45678
61981
200
2900
3500
1100
1600
45700
62000
…100
3456
5349
89231
37849
32489
49838
71974
3000
5000
89000
38000
32000
50000
72000
…1000
…whole number
2.7
4.2
10.4
3
4
10
27.9
7.67
33.37
28
8
33
31.436
764.92
0.86
31
765
1

17. © T Madas
Round these numbers to the nearest…
78
67
181
125
1343
3787
1998
80
70
180
130
1340
3790
2000
…10
279
2557
23107
16915
1850
49805
61041
300
2600
23100
16900
1900
49800
61000
…100
76532
64543
37859
90832
98114
89575
70456
77000
65000
38000
91000
98000
90000
70000
…1000
…whole number
2.8
8.2
11.4
3
8
11
37.9
7.17
39.67
38
7
40
37.685
344.02
0.81
38
344
1

18. © T Madas
Quick Test
on Rounding
to the nearest…

19. © T Madas
Round these numbers to the nearest…
48
87
184
145
1563
3217
2005
50
90
180
150
1560
3220
2010
…10
209
2867
3467
1095
1550
45678
61981
200
2900
3500
1100
1600
45700
62000
…100
3456
5349
89231
37849
32489
49838
71974
3000
5000
89000
38000
32000
50000
72000
…1000
…whole number
2.7
4.2
10.4
3
4
10
27.9
7.67
33.37
28
8
33
31.436
764.92
0.86
31
765
1

20. © T Madas
Round these numbers to the nearest…
78
67
181
125
1343
3787
1998
80
70
180
130
1340
3790
2000
…10
279
2557
23107
16915
1850
49805
61041
300
2600
23100
16900
1900
49800
61000
…100
76532
64543
37859
90832
98114
89575
70456
77000
65000
38000
91000
98000
90000
70000
…1000
…whole number
2.8
8.2
11.4
3
8
11
37.9
7.17
39.67
38
7
40
37.685
344.02
0.81
38
344
1

21. © T Madas

22. © T Madas
We look at the 1
st
decimal place
•If it is 0, 1, 2, 3 or 4 we just throw all the decimal
digits away
•If it is 5, 6, 7, 8 or 9 we throw all the decimal
digits away and we increase the units by 1
Rounding decimals… to the nearest whole
number
Examples:
23.7 24
8.94 9
53.6 54
3.52 4
1.768 2
20.32 20
5.8757 6
40.071 40

23. © T Madas
We look at the 2
nd
decimal place
•If it is 0, 1, 2, 3 or 4 we just throw the 2
nd
, the 3
rd
, the
4
th
… decimal digits away
•If it is 5, 6, 7, 8 or 9 we throw the 2
nd
, the 3
rd
, the 4
th

… decimal digits away and we increase the 1
st

decimal digit by 1
Rounding decimals… to one decimal place
Examples:
3.734 3.7
8.294 8.3
9.16 9.2
6.52 6.5
5.728 5.7
41.32 41.3
5.8757 5.9
40.071 40.1

24. © T Madas
We look at the 3
rd
decimal place
•If it is 0, 1, 2, 3 or 4 we just throw the 3
rd
, the 4
th
, the
5
th
… decimal digits away
•If it is 5, 6, 7, 8 or 9 we throw, the 3
rd
, the 4
th
, the 5
th

… decimal digits away and we increase the 2
nd

decimal digit by 1
Rounding decimals… to two decimal places
Examples:
3.7342 3.73
5.2863 5.29
0.1605 0.16
2.5782 2.58
5.7028 5.70
4.3592 4.36
5.8957 5.90
4.9971 5.00

25. © T Madas
Practice Rounding
to Decimal Places

26. © T Madas
0.49978
8.5328
3.5004
4.089623
6.40078
5.36581
0.10704
1.48173
2.2258
9.2341
Round the following numbers to 1 decimal places
0.49878
7.3058
2.585423
0.46878
2.3553
9.48973
1.3173
8.75438
4.6751
1.56437
6.39745
5.471
3.117
1.8671.9
5.5
0.43456
6.4
5.245567
0.9034
1.6
4.7
8.8
2.724
1.32
9.49
4.1424
2.36
0.47
3.5024
2.59
7.31
0.50
2.226
1.482
5.366
6.401
4.090
8.533
0.500
23

27. © T Madas
Quick Test
on
Number Rounding
to
Decimal Places

28. © T Madas
5.36581
0.10704
1.48173
2.2258
9.2341
Round the following numbers to decimal places
2.3553
9.48973
1.3173
6.39745
5.471
3.117
1.8671.9
5.5
0.43456
6.4
2.724
1.32
9.49
4.1424
2.36
2.226
1.482
5.366
1 d.p. 2 d.p. 3 d.p.

29. © T Madas
Round the following numbers to decimal places
1 d.p. 2 d.p. 3 d.p.
0.49978
8.5328
3.5004
4.089623
6.40078
0.49878
7.3058
2.585423
0.46878
8.75438
4.6751
1.56437
5.245567
0.9034
1.6
4.7
8.8
0.47
3.5024
2.59
7.31
0.50
6.401
4.090
8.533
0.500

30. © T Madas