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Decimal Rule
Addition of Decimals
Subtraction of Decimals
Multiplication of Decimals
Round decimals
100

How do you round decimals

Look at which number it is asking us to round, go one column to the right then if 4 or below round down, 5 or up round up. 

100
58.9 + 3.04 =
61.94
100
3.95 - 2.7 =
1.25
100
.6 x 2.1 =
1.26
100

Round 2.34 to one DP

2.3

200

How do you add decimals?

Line up numbers by place value, lining up decimal points.  Add normally and drop the decimal straight down into the sum.

200
.004 + 5.1 =
5.104
200
95.29 - 1.3 =
93.99
200
4.25 x 21 =
89.25
200
Round 4.654 to 2 decimal place

4.65

300

How do you subtract decimals?

Line up numbers by place value, lining up decimal points.  Subtract normally, borrowing when necessary and drop the decimal straight down into the difference.

300
.9843 + 2.67 =
3.6543
300
125 - .68 =
124.32
300
.03 x .03 =
.0009
300

Round 1.23 to 2 SF

1.2

400

What do you do if, after lining up by place value, there are not enough digits in the top number to subtract a problem?

Annex zeros.

400
5 + 2.78 + .030 =
7.81
400
.468 - .059 =
.409
400
2.003 x .05 =
.10015
400
ROUND 18.6504 TO 3 sf

18.7

500

How do you multiply decimals?

You ignore the decimal point and then multiply the numbers.  When finished, count the number of decimal numbers in each of the factors to find how many decimal numbers will be in the product.

500
8.07 + .0976 + 23.3 + 48 =
79.4676
500
5.45 - 3.799 =
1.651
500
.312 x 1.67 =
.52104
500

Round 18.098 TO 3 sf

18.1