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78 Speed Math for Kids
$2.50 represents 2 dollars and 50 hundredths of a dollar. Th e
fi rst digit after the decimal represents tenths of a dollar. (Ten 10¢
coins make a dollar.) Th e second digit after the decimal represents
hundredths of a dollar. (One hundred cents make a dollar.) So
$2.50, or two and a half dollars, is the same as 250¢. If we wanted
to multiply $2.50 by 4, we could simply multiply the 250¢ by 4 to
get 1,000¢. One thousand cents is the same as $10.00.
Digits after a decimal point have place values as well. Th e number
3.14567 signifi es three ones, then after the decimal point we have
one tenth, four hundredths, fi ve thousandths, six ten-thousandths,
and so on. So $2.75 equals two dollars, seven tenths of a dollar and
fi ve hundredths of a dollar.
To multiply a decimal number by 10, we simply move the decimal
point one place to the right. To multiply 1.2 by 10, we move the
decimal one place to the right, giving an answer of 12. To multiply
by 100, we move the decimal two places to the right. If there
aren’t two digits, we supply them as needed by adding zeros. So,
to multiply 1.2 by 100, we move the decimal two places, giving an
answer of 120.
To divide by 10, we move the decimal one place to the left. To
divide by 100, we move the decimal two places to the left. To divide
14 by 100, we place the decimal after the 14 and move it two places
to the left. Th e answer is 0.14. (We normally write a 0 before the
decimal if there are no other digits.)
Now, let’s look at general multiplication of decimals.
MULTIPLICATION OF DECIMALS
Multiplying decimal numbers is no more complicated than
multiplying any other numbers. Let us take an example of 1.2 ×
1.4.