Page 107 - ICSE Math 5

Example 13: Multiply the following.
(a) 15.245 × 10 (b) 89.2081 × 100 (c) 4.1763 × 1,000

× 10
Solution: (a) 15.245 × 10 = 152.45

(15.245 152.45)

× 100
(b) 89.2081 × 100 = 8,920.81

(89.2081 8,920.81)

× 1,000
(c) 4.1763 × 1,000 = 4,176.3

(4.1763 4,176.3)

Multiplication of a Decimal Number by a Whole Number

Multiplication of a decimal number by a whole number is similar to multiplication of whole
numbers. However, we need to place the decimal point correctly.

To multiply a decimal number by a whole number, we follow the given steps.
• Ignore the decimal point and multiply the given numbers as we multiply any two whole
numbers.
• Count the digits after the decimal point in the given decimal number.
• Starting from the extreme right of the product obtained, move towards the left counting
the number of digits obtained in the above step and place the decimal point.

Example 14: Find the product of 52.65 and 17.

1 4 3 Top Tip
Solution: 5 2 6 5
× 1 7 On multiplying a decimal number by a
whole number, the number of decimal
1 1 places in the product remains the same
3 6 8 5 5
as in the decimal number.
+ 5 2 6 5 0
8 9 5 0 5

Since the multiplicand has 2 decimal places, the product obtained must also have
2 decimal places. So, we will place the decimal point before two digits from the
extreme right of the product.
So, 52.65 × 17 = 895.05.

Multiplication of a Decimal Number by a Decimal Number

To multiply any two decimal numbers, we follow the given steps.
• Ignore the decimal points and multiply the given numbers as we multiply any two whole
numbers.

97