Class 7 Maths Fractions and Decimals Multiplication of Decimal Numbers

Multiplication of Decimal Numbers

Multiplication of decimal numbers

When two decimal numbers are multiplied, we simply multiply the numbers (without their decimal points)

Then we count the total number of digits after the decimal point, taking both the decimal numbers.

The decimal point is placed in the product such that the total number of digits after the decimal point is equal to the total number obtained in step 2.

When a decimal number is multiplied by 10, 100 or 1000, the digits in the product are same as in the decimal number but the decimal point in the product is shifted to the right by as , many of places as there are zeros over one.

Problem: Multiply the following:a) 0.2 x 6  b) 2.71 x 5  c) 156.1 x 100

Solution:

0.2 × 6

We will multiply the numbers simply, without the decimal points. We get :

= 2*6  =12

The total number of digits after decimal point, taking into account both numbers is 1.

Hence, the decimal will be placed in the product such that the number of digits after the decimal point is 1. We get :

          = 1.2

The answer is 1.2.

 

2.71 × 5

We will multiply the numbers simply, without the decimal points. We get :

= 271*5 =1355

The total number of digits after decimal point, taking into account both numbers is 2.

Hence, the decimal will be placed in the product such that the number of digits after the decimal point is 2. We get :

          = 13.55

The answer is 13.55.

156.1 × 100

We will multiply the numbers simply, without the decimal points. We get :

= 1561*100 =156100.

The total number of digits after decimal point, taking into account both numbers is 1.

Hence, the decimal will be placed in the product such that the number of digits after the decimal point is 1. We get :

          = 15610.0

 The answer is 1561.

 

Problem: A two-wheeler covers a distance of 55.3 km in one litre of petrol. How much distance will it cover in 10 litres of petrol?

Distance covered in one litre petrol = 55.3 kms

Distance covered in ten litre petrol = 55.3*10 kms

= 553.0 kms

 The answer is 553 kms.

 

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