Multiplying Decimals

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Decimals Units

When multiplying decimals forget the decimal points and multiply the whole numbers together.
eg. 1. 0.8 x 0.4
           8 x    4
           32.0
Then workout how many decimal places are there in the problem. In the above example there are two decimal places.
So in the answer there should also be two decimal places.
Now move the decimal point two places to the left to get your final answer.

eg. 1. 0.8 x 0.4 = 0.32

eg. 2. 0.3 x 0.04
In this problem there are three decimal places. Therefore the final answer should have three decimal places.
          0.3 x 0.04
             3 x    4
             12
This number has only two digits. But the answer should have three decimal places.
So you must add a zero to the left of the number to make a third decimal place.
         ie. 0.3 x 0.04 = 0.012

When multiplying a decimal by 10, 100 or 1000
move the decimal point 1, 2 or 3 places to the right just as in these examples.
(i)           8.34 x 10     = 83.4 (decimal point 1 place to the right)

(ii)          8.23 x 100   = 823 (decimal point 2 places to the right)

(iii)         8.53 x 1000 = 8530 (decimal point 3 places to the right)

Examples

1. Evaluate 2.38 x 0.2
Step 1. Forget the decimal points and multiply the numbers together.
              238 x 2 = 476

Step 2. Add the total number of decimal places after the decimal point in both numbers.
              2.38          2 decimal places
              0.2            1 decimal place
              Altogether there are 3 decimal places.

Step 3. Place the decimal point in the answer so that there are three decimal places after the
              point.

            2.38 x 0.2 = 0.476

2.Evaluate 2.5 x 0.8
Step 1. Forget the decimal points and multiply the numbers together.
              25 x 8 = 200

Step 2. Add the total number of decimal places after the decimal point in both numbers.
               2.5          1 decimal place
               0.8          1 decimal place
               Altogether there are 2 decimal places.

Step 3. Place the decimal point in the answer so that there are two decimal places after the
              point.

               2.5 x 0.8 = 2.00
                                 = 2

3. Evaluate 9 x 0.3682
Step 1. Forget the decimal points and multiply the numbers together.
              9 x 3682 = 33138

Step 2. Add the total number of decimal places after the decimal point in both numbers.
              9                   0 decimal place
              0.3682          4 decimal places

Step 3. Place the decimal point in the answer so that there are four decimal places after the
              point.

             9 x 0.3682 = 3.3138

Have a Go

Problem 1

Evaluate 12 x 2.31

Problem 2

Evaluate 2.5 x 0.084

Practice Questions

Question 1
Evaluate 2.34 x 1000

Question 2
Evaluate 0. 56 x 10000

Question 3
Evaluate 0.24 x 30

Question 4
Evaluate 1.25 x 1.2

Question 5
Evaluate 5.5 x 2.01

Question 6
Evaluate 8.25 x 0.022

Solution 1
12 x 2.31
12 x 231 = 2772
12 x 2.31 = 27.72

back to Have a Go

Solution 2
2.5 x 0.084
25 x 84 = 2100
2.5 x 0.084 = 0.2100
= 0.21 (You can leave out the zeros at the end.)

back to Have a Go

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