Chris Clements

1
21
99
Rounding
To the nearest 10
12
57
Chris Clements
2
ltdategt
Learning Objective
ltLearning Objectivegt
3
Rounding
Rounding is used to approximate or estimate.
Numbers are usually rounded to the nearest 10,
100, 1000, 10 000, 100 000 or even a 1, 000 000.
Decimals can also be rounded, usually to the
nearest tenth, hundredth, thousandth
4
Rounding whole numbers
Whole numbers (also called integers) are
counting numbers e.g. 1, 2, 3, 4
Negative numbers are also whole numbers e.g. -1,
-2, - 3
Decimals are not whole numbers e.g. 0.4, 7.4,
2.36, 7.32
Decimals are not whole numbers e.g. 0.4, 7.4,
2.36, 7.32
Fractions are not whole numbers e.g. ½ 2 ¾, 25 ¼
5
Rounding to the nearest 10
Steps to success

• When rounding to the nearest 10 there are three
  main things to remember
• Identify the units digit.
• If the units digit is a 1, 2, 3 or 4 we round
  down.
• If the units digit is a 5, 6, 7, 8, or 9 we
  round up.

continued
6
Lets see how well you are doing.
REMEMBER Step 1!

1. Identify the units digit.

7
7
5
2
2
2
8
7
2
8
9
.
1
1
8
5
7
Onto the next step. Can you remember it?
2) If the units digit is a 1, 2, 3 or 4 we round
down.


12
10
20
2
1
2
1
0
round down


60
50
54
4
5
4
5
0
round down
continued
8
Now for the final step. Can you remember it?
3) If the units digit is a 5, 6, 7, 8, or 9 we
round up.


10
17
20
1
7
7
2
0
round up


40
50
45
4
5
5
5
0
round up
continued
9
Lets have a go at these


20
27
30
2
7
7
3
0
round up


70
71
80
7
round down
1
1
7
0


80
85
90
8
5
5
9
0
round up
continued
10


40
43
50
4
round down
3
3
4
0


34
30
40
3
round down
4
4
3
0


40
48
50
4
8
8
5
0
round up


90
95
100
5
9
5
0
0
1
round up
11
Activity
lttype heregt
12
Plenary
90 bricks (9packs of 10)
At a builders yard bricks are sold in packs of
ten. Jim wants 87 bricks to fix a broken wall.
How many bricks must he buy?
He would be 4 bricks short and will need to
go back again!
He would be 4 bricks short and will need to
go back again!
If Jim went to buy 14 more bricks, what would
happen if he rounded down to 10 and bought one
more pack?
360
Round 356 to nearest 10
What makes these more difficult?
2730
Round 2732 to nearest 10