S0T1 Decimals and Four Operations of Decimals

Decimals - Refresh/Recall

Recurring Decimals

Example           4/9 =0.444…

The ... indicates that 4 repeats indefinitely.

Non-recurring decimals

Example:            ¼ = 0.25

Four Operations of Decimals

Addition and Subtraction

** Align the decimal points (one above another) when adding and subtracting **

Example

Evaluate the following:

            12.2 + 1.43

Step 1: Arrange the numbers, aligning the decimals

            12.2

            + 1.43

Step 2: Do the + /           

            12.20   **Fill 0s to the same position as the other number

            + 1.43

             13.63

Example

Find the value of 28.3 – 1.676 – 12.57

Step 1: Arrange the numbers, aligning the decimals

            28.3

           -   1.676

Step2: Do the + /        

              _{7 12 9}   

            28.30¹0                        **Fill 0s to the same position as the other number

           -   1.67 6

                 ₅ 

            26.6¹24

           - 12.5 70

            14.054      

Multiplication and Division

Example

Find the value of 26.2 x 2.1

Step 1: Arrange the number for multiplication

            26.2

           x  2.1

              262

          + 524

5502

Step 2: Count the decimal place/s in both numbers

            26.2 => 1 decimal place

            2.1 => 1 decimal place

            Total 2 decimal places

Step 3: Place decimal places, counting from the right

            26.2

           x  2.1

              262

          + 524

          55.02

               ^{2 1}

Practice

1.  Arrange the following numbers in ascending order

a.  5.2, 5.204, 5.25

b.  8.91, 8.903, 8.95

2.   Find the value of 

a.   1.23 x 4.5

b.    254.8 + 39.05 - 24.3

c.    2(2.5 + 1.5) - (4.8 - 7)

d.    40.6 ÷ 2.2