RULE.--Multiply as in whole numbers, and point off from the right of the
product as many places as there are decimal places in both multiplier
and multiplicand--prefixing ciphers if necessary.
EXAMPLE 1: Multiply 87.432 by 564.
87.432
564
---------
43716.0
5245.92
349.728
---------
49311.648 _Ans._
Place the multiplier so that its unit’s digit comes under the right-hand
digit of the multiplicand. Then place the first figure of each product
underneath the multiplying digit. The decimal point of the answer will
then be directly under the decimal point of the multiplicand.
EXAMPLE 2: Multiply 31.56 by 5.49.
31.56
5.49
--------
157.80
12.624
2.8404
---------
173.2644 _Ans._
As before, place the unit’s figure of the multiplier--that is, the
5--under the right-hand digit of 31.56, and proceed as above.
Note.--The number of decimal places in the product will always be equal
to the sum of the number of decimal places in the multiplier and the
multiplicand. Thus, in Example 2, there are two places of decimals
(_i.e._ two figures to the right of the point) in 31.56, and two places
of decimals in 5.49; and we found 2 + 2 = 4 places in the product
173.2644.
To multiply a decimal by 10, 100, etc.
Rule.--Remove the (.) as many places to the right as there are ciphers
in the multiplier.
Work: 8.75 × 10 = 87.5
8.75 × 100 = 875.
8.75 × 1000 = 8750.