Page 47 - ICSE Math 7

Example 8: Multiply.
(a) 5.034 by 21 (b) 0.061 by 0.025

Solution: (a) Multiply 5034 by 21. (b) Multiply 61 by 25.
5034 61
× 21 × 25
5034 305
10068× 122×

105714 1525
Total number of decimal places = 3 Total number of decimal places
So, put a decimal point 3 places = 3 + 3 = 6
from right in the product. But the product has only 4 digits.
Thus, 5.034 × 21 = 105.714 Therefore, add 2 zeros to the left of
the product and put a decimal point 6
places from the right in the product.
Thus, 0.061 × 0.025 = 0.001525
Multiplication of decimals by powers of 10
While multiplying a decimal number by 10, 100, 1,000, etc., just shift the decimal point to the right
as many places as there are number of zeros in the multiplier. If the number of decimal places in the
given number is less than the number of zeros in the multiplier, then add zeros to the right of the
given number.
Example 9: Multiply.
(a) 8.34 × 100 (b) 0.239 × 10,000
Solution: (a) 8.34 × 100 = 834
(As there are 2 zeros in 100, therefore shift the decimal point 2 places to the right)
(b) 0.239 × 10,000 = 2,390
(Add zeros to the right so that the decimal point can be shifted 4 places)

Division of decimals
Division of a decimal number by a natural number

Divide the decimal number (dividend) by the given number ignoring the decimal point. Place the
decimal point in the quotient when the first digit after the decimal point, i.e., tenths place is used for
division. Complete the division by adding as many zeros as required on the right side of the dividend.

Example 10: Divide.
(a) 13.44 by 7 (b) 112.4 by 8
1.92
Solution: (a) 7 13.44 Alternative method:
–7 13.44 ÷ 7 = 1344 × 1
64 100 7
–63 192
14 = 100
–14 = 1.92
×

So, 13.44 ÷ 7 = 1.92

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