1. Rounding Numbers
Part 1
© T Madas

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

3. Rounding to the nearest 10
Round 37 to the nearest 10 30 37 40 40
The rounded number must have a zero at the end
© T Madas

4. Rounding to the nearest 10
Round 154 to the nearest 10
150
150
154
160
The rounded number must have a zero at the end
© T Madas

5. Rounding to the nearest 10
Round 125 to the nearest 10
120
125
130
130
When our number lies halfway between “tens”, we have agreed to round the number up.
© T Madas

6. 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 68 70 94 90
132
130
146
150
565
570
305
310
481
480
© T Madas

7. Rounding to the nearest 100
Round 764 to the nearest 100
764
700
800
800
The rounded number must have 2 zeros at the end
© T Madas

8. Rounding to the nearest 100
Round 1235 to the nearest 100
1235
1200
1200
1300
The rounded number must have 2 zeros at the end
© T Madas

9. Rounding to the nearest 100
Round 850 to the nearest 100
800
850
900
900
When our number lies halfway between “hundreds”, we have agreed to round the number up.
© T Madas

10. Rounding to the nearest 100
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
1168
1200
874
900
2032
2000
536
500
5750
5800
350
400
40081
40100
© T Madas

11. Rounding to the nearest 1000
Round 7761 to the nearest 1000
7761
7000
8000
8000
The rounded number must have 3 zeros at the end
© T Madas

12. Rounding to the nearest 1000
Round 8339 to the nearest 1000
8339
8000
8000
9000
The rounded number must have 3 zeros at the end
© T Madas

13. Rounding to the nearest 1000
Round 6500 to the nearest 1000
6000
6500
7000
7000
When our number lies halfway between “thousands”, we have agreed to round the number up.
© T Madas

14. Rounding to the nearest 1000
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
1868
2000
4874
5000
2499
2000
5376
5000
29780
30000
7500
8000
45681
46000
© T Madas

15. Practice Rounding
to the nearest…
© T Madas

16. Round these numbers to the nearest…
…10
…100
…1000 48 87
184
145
1563
3217
2005 50 90
180
150
1560
3220
2010
209
2867
3467
1095
1550
45678
61981
200
2900
3500
1100
1600
45700
62000
3456
5349
89231
37849
32489
49838
71974
3000
5000
89000
38000
32000
50000
72000
…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
© T Madas

17. Round these numbers to the nearest…
…10
…100
…1000 78 67
181
125
1343
3787
1998 80 70
180
130
1340
3790
2000
279
2557
23107
16915
1850
49805
61041
300
2600
23100
16900
1900
49800
61000
76532
64543
37859
90832
98114
89575
70456
77000
65000
38000
91000
98000
90000
70000
…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
© T Madas

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

19. Round these numbers to the nearest…
…10
…100
…1000 48 87
184
145
1563
3217
2005 50 90
180
150
1560
3220
2010
209
2867
3467
1095
1550
45678
61981
200
2900
3500
1100
1600
45700
62000
3456
5349
89231
37849
32489
49838
71974
3000
5000
89000
38000
32000
50000
72000
…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
© T Madas

20. Round these numbers to the nearest…
…10
…100
…1000 78 67
181
125
1343
3787
1998 80 70
180
130
1340
3790
2000
279
2557
23107
16915
1850
49805
61041
300
2600
23100
16900
1900
49800
61000
76532
64543
37859
90832
98114
89575
70456
77000
65000
38000
91000
98000
90000
70000
…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
© T Madas

21. Rounding Numbers
Part 2
© T Madas

22. Rounding decimals… to the nearest whole number
We look at the 1st 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
Examples:
23.7 24
1.768 2
8.94 9
20.32 20
53.6 54
5.8757 6
3.52 4
40.071 40
© T Madas

23. Rounding decimals… to one decimal place
We look at the 2nd decimal place
If it is 0, 1, 2, 3 or 4 we just throw the 2nd, the 3rd, the 4th … decimal digits away
If it is 5, 6, 7, 8 or 9 we throw the 2nd, the 3rd, the 4th … decimal digits away and we increase the 1st decimal digit by 1
Examples:
3.734
3.7
5.728
5.7
8.294
8.3
41.32
41.3
9.16
9.2
5.8757
5.9
6.52
6.5
40.071
40.1
© T Madas

24. Rounding decimals… to two decimal places
We look at the 3rd decimal place
If it is 0, 1, 2, 3 or 4 we just throw the 3rd, the 4th, the 5th … decimal digits away
If it is 5, 6, 7, 8 or 9 we throw, the 3rd, the 4th, the 5th … decimal digits away and we increase the 2nd decimal digit by 1
Examples:
3.7342
3.73
5.7028
5.70
5.2863
5.29
4.3592
4.36
0.1605
0.16
5.8957
5.90
2.5782
2.58
4.9971
5.00
© T Madas

25. Practice Rounding
to Decimal Places
© T Madas

26. Round the following numbers to 1 decimal places 3 2
3.117
2.724
9.2341
1.867
1.9
1.3173
1.32
2.226
2.2258
5.5
5.471
9.49
1.482
4.1424
6.4
2.36
2.3553
5.366
0.47
6.401
1.6
2.59
4.090
4.6751
4.7
3.5024
3.5004
0.9034
7.31
7.3058
8.533
8.5328
8.8
0.50
0.500
© T Madas

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

28. 1 d.p. 2 d.p. 3 d.p. Round the following numbers to decimal places
3.117
2.724
9.2341
1.9
1.867
1.32
1.3173
2.2258
2.226
5.5
5.471
9.49
1.482
4.1424
6.4
2.36
2.3553
5.366
© T Madas

29. 1 d.p. 2 d.p. 3 d.p. Round the following numbers to decimal places
0.47
6.401
1.6
2.59
4.090
4.7
4.6751
3.5024
3.5004
0.9034
7.31
7.3058
8.533
8.5328
8.8
0.50
0.500
© T Madas

30. © T Madas