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© T Madas
© T Madas
Sometimes we have to round numbers
What does rounding mean?
Can you think of some examples?
© 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
© 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
© 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.
© T Madas
Rounding to the nearest 10Numbers ending in 1, 2, 3 and
4 get rounded downNumbers 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
© 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
© T Madas
12001200
The rounded number must have 2 zeros at the end
Round 1235 to the nearest 100
13001235
Rounding to the nearest 100
© 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
© T Madas
Numbers ending in 0s, 10s, 20s, 30s and 40s get rounded downNumbers 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
© 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
© T Madas
80008000
The rounded number must have 3 zeros at the end
Round 8339 to the nearest 1000
90008339
Rounding to the nearest 1000
© 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
© T Madas
Numbers ending in 00s, 100s, 200s, 300s and 400s get rounded downNumbers 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
© T Madas
Practice Roundingto the nearest…
© 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 number2.7
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
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 number2.8
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
Quick Teston Roundingto the nearest…
© 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 number2.7
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
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 number2.8
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
© T Madas
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
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
© T Madas
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
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
© T Madas
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
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
© T Madas
Practice Roundingto Decimal Places
© 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
© T Madas
Quick TestonNumber RoundingtoDecimal Places
© 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.
© 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
© T Madas