It's obvious that every normal person has ten fingers. Since we have
ten fingers, our numbering is based on multiples of ten which is called
decimal. Can you imagine how life would be different if all human
beings were born with eight fingers instead of ten? Maybe our numbering
system would be based on multiples of eight. A numbering system based
upon eight exists and is called octal. Octal numbering is used behind
the scenes in computer systems.
But, of course, in everyday life we use decimal numbers. The idea
of decimal numbering comes to us from the ancient civilizations and
we still use the numbering based on tens from the Romans. The Roman
numeral for ten is X and 20 is XX or 2 times 10. You still see Roman
numerals in dates on buildings and movies and each year the Super
Bowl gets the next Roman number.
Our decimal numbering, using Arabic numerals instead of Roman numerals,
also uses multiples of 10, so 40 means 4 times 10. But you already
know that! The other interesting part of decimals is how decimals
are used to represent fractions. Way back in 1616, a Scottish mathematician
named John Napier suggested that decimal numbering could be used to
show fractions and he added the decimal point. Numbers to the left
of the decimal point would stand for whole numbers and numbers on
the right side would indicate the fractional part.
So the number 1.6 would be 1.5 in decimal. Wait a minute, how did
we get a 5 for that? Since we're using 10 as the base of decimal, half
of 10 equals 5. Similarly, the fraction becomes 0.25 and becomes
0.75. The picture is a little more complicated when you look at 1/3.
If you divide 1 by 3 on your calculator you get the decimal value
0.333 with three filling the screen. That's because there isn't a
complete equivalent decimal number for 1/3. You have to understand
how many digits to the right of the decimal point, called the precision
of the decimal number, to use.
Scientists and engineers use decimal numbers all the time in calculations.
When you study advanced science topics in high school and college
you will learn why the precision of a decimal number is so important
For you though decimals are easier to use in arithmetic operations
than fractions are. Think about multiplying 1 by 6. It's easier
to multiply 1.75 by 6.5! In fact, think about your calculator. You
never see fractions on a calculator. When you do computations on the
calculator, you always use decimal numbers.
Now that we've reviewed what decimals mean and a little bit about
how they work, can you think of some examples of how you use decimals
in your life? That should be easy.
Money, money, money! There are 100 pennies in a dollar and a half
dollar is 50 cents or .50. Every time you buy an item and make change,
you are working with decimals. Have you ever noticed how many prices
end in .98 or .99? That's so you think that the item costs less than
it does. For example, which seems like less money $1.99 or $2?
Of course, $1.99 is less money by a penny but when companies try
to get you to buy something, that penny makes a difference because
you consider what is to the left of the decimal to be more important.
So you will be comparing $1 with $2 and that seems like a big difference.
Decimals show up in lots of other places in daily life as well. Every
gas pump shows two sets of decimal numbers, the amount of gas you
bought as a decimal and the amount of money you owe. And your gas
mileage in miles per gallon is always shown as a decimal number.
Look at the car's odometer; the miles on it are always shown in decimal
too. Talking about cars and mileage, have your parents ever used MapQuest
to get directions? All mileage in these standard directions are shown
as decimal too.