Multiplication by 10, 100, 200, 300.....

Remember: When a number is multiplied by 10, simply add one zero to the right of a number to get the product.

Example 5:

9 × 10 = 90

99 × 10 = 990

9900 × 10 = 99000

When a number is multiplied by the multiples of 10 like 20, 30, 40, etc., follow the steps below to get the product.

Step 1: Multiply the number first by the digit at tens place.

Step 2: Add zero to the right of the product obtained from step 1.

Example 6:

4 ⨯ 20 = (4 ⨯ 2) ⨯ 10 = 8 ⨯ 10 = 80

11 ⨯ 30 = (11 ⨯ 3) ⨯ 10 = 33 ⨯ 10 = 330

Remember: When a number is multiplied by 100, simply add 2 zeroes to the right of a number.

Example 7:

7 ⨯ 100 = 700

99 ⨯ 100 = 990

825 ⨯ 100 = 82500

When a number is multiplied by the multiples of 100 like 200, 300, etc., follow the steps below to get the product

Step 1: Multiply the multiplicand by the digit at hundreds place of the multiplier.

Step 2: Add two zeroes to the right of the product obtained from step 1.

Example 8:

4 × 200 = (4 × 2) × 100 = 8 × 100 = 800

111 × 600 = (111 × 6) × 100 = 666 × 100 = 66600

Remember: When a number is multiplied by 1000, simply add three zeroes to the right of a number.

Example 9:

7 × 1000 = 7000

70 × 1000 = 70000

When a number is multiplied by the multiples of 1000, i.e. 2000, 3000, etc., follow the steps below to get the product.

Step 1: Multiply the multiplicand by the digit at the thousands place of the multiplier.

Step 2: Add three zeroes to the right of the product obtained from step 1.

Example 10:

3 × 2000 = (3 × 2) × 1000 = 6000

40 × 2000 = (40 × 2) × 1000 = 80,000

11 × 7000 = (11 × 7) × 1000 = 77,000

55 × 2000 = (55 × 2) × 1000 = 1,10,000

Exercise 4.2

A. Write down the product as fast as you can.

1.	6 ⨯ 10		________________
2.	8 ⨯ 100		________________
3.	4 ⨯ 300		________________
4.	51 ⨯ 100		________________
5.	85 ⨯ 1000		________________
6.	97 ⨯ 1000		________________

B. Multiply

1.	14 ⨯ 10		________________
2.	55 ⨯ 60		________________
3.	34 ⨯ 70		________________
4.	53 ⨯ 200		________________
5.	60 ⨯ 300		________________
6.	750 ⨯ 400		________________
7.	200 ⨯ 800		________________
8.	839 ⨯ 4000		________________
9.	109 ⨯ 5000		________________
10.	211 ⨯ 4000		________________
11.	160 ⨯ 5000		________________
12.	905 ⨯ 2000		________________

Example 11:

There are 50 pebbles in one bag. How many pebbles are there in 10 such bags?

Pebbles in one pack = 50

Pebbles in 10 packs = 50 × 100= 5,000

There are 5,000 pebbles in 10 bags.

Example 12:

A city is divided into sectors. Each sector has a population of approximately 600 people. Find the approximate population of the city if there are 153 sectors?

Number of people in one sector = 600

Number of sectors when rounded off = 150

Approximate population of the city = 150 × 600= 15 × 6 × 1000 = 90 × 1000 = 90,000

Exercise 4.3

1.Average weight of elephants is 5,400 kilograms. Find the weight of 20 such elephants.

2.My maths textbook has 275 pages. How many pages are there in 11 such textbooks?

3.Cost of one fit bit watch is ₹ 950. Find the cost of 453 watches.

4.A chocolate factory produces 650 chocolate bars in an hour. How many chocolate bars will the factory produce in 10 days?

5.What is the total cost of painting 356 windows, if the cost of painting one window is ₹ 250?

6.Basketball coaching fee for each student is ₹ 650. Find the fee for 550 students.

Think and Answer

Multiply by grouping.

1. 123 ⨯ 5 ⨯ 2 = ___

2. 387 ⨯ 25 ⨯ 4 = ___

3. 50 ⨯ 2 ⨯ 783 = ___

4. 40 ⨯ 5 ⨯ 89 = ___