Decimal multiplication

Decimal multiplication is just like normal multiplication, only thing is we have to put the decimal point in the proper place.

This type of multiplication can be done in the following steps.

Step1: Let us multiply normally without the decimal point.

Step2: Count the number of digits in each number after the decimal point.

Step3: Place the decimal point in the answer counting from the right, the number of digits equal to the sum of the digits after the decimal point in both the numbers. Now let us see some examples using decimal multiplicaton.

Example1: Multiply 2.8 by 3

Solution:

Step1:  Multiply normally as if the decimal point is not there.

             
                       2.8

                     x    3

                    ---------

                         84

Step2:

2.8=>only one digit after the point 

3  => no digit after the decimal point as 3 is a whole number.

The sum of number of digits after the decimal point in both the numbers =0+1=1

Place the decimal point in the answer starting from the right.

So the answer is 8.4


Multiply 0.07 and 2.2

Solution:

Step1: Multiply the numbers normally.

(here we have 0.07 as the first number, so will multiply with only 7)

                             7

                      x    22

                     --------

                          154

Step2: Count the number of digits after the decimal point in both the numbers.

0.07=> number of digits after the decimal point =2

2.2  => Number of digits after the decimal point =1

                                                         Total =3

Place the decimal point in the answer starting from the right.

Note: Here we have only 3 digits in the answer.

So the answer is 0.154


Example 3:

Multiply 0.26 and 0.13

Solution:

Step1: Multiply the numbers normally.  

(we will multiply without the decimal point)            

Step2: Count the number of digits after the decimal point in both the numbers.

0.26 => number of digits after the decimal point = 2

0.13 => number of digits after the decimal point = 2

                                                Total          = 4

Place the decimal point in the answer starting from the point.

Note: Here we have only 3 digits in the answer, put total number of digits after the point is 4. So we must add one '0' before the decimal point.

The answer is    0.0338

When we are multiplying a decimal number by the exponents of 10, the easiest way is

Add number of '0's as in the exponents of 10 with the given number, after that place the decimal point starting from the right according to the number of digits in the number.


Multiply 3.8 and 100

Solution: 3.8 x 100 = 380

We can word problems on the following links 1,2,3,4,5 and 6

Practice problems of decimal multiplication:

  1. Multiply 3.57 and 2.8
  2. Multiply 0.05by 0.76
  3. Find the area of rectangular field whose dimensions are
                          Length = 7.8 cm                                                                   Width   = 5.2 cm
  4. Multiply :6.789x100
  5. Multiply :56.7x1000

Those are the examples of decimal multiplication.







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