IV.  Percentages

So, why do we use percentages?  The assumption is that we use a base ten numbering system because we have ten fingers.  You know that in order to add fractions together, you need to find a common denominator.  Because of this, fractions are kind of a pain.  Enter decimals and percentages.

If you divide the denominator (bottom part) of a fraction into the numerator (top part) you turn the fraction into a decimal.   1/4 = 1 divided by 4, or 0.2500...  

Dividing things into 10 parts, doesn't seem to be enough, and dividing things into 1000 parts seems a bit excessive.  So, we decided to divide things into 100 parts.  100% = 1.  Want to get a definition from Webster?

Percentages vs Not 

We use percentages in a lot of different things.  Your score on homework or on a test is usually given as a percent.  If it's not, then the grade you get is based on a range like from 90 to 100% is an A.  They come up when figuring odds or comparing almost anything that can be digitally converted.

A red percent sign being moved by a cartoon silhouette of a man.


So to convert into a percent, divide the denominator into the numerator to get a decimal.  Keep in mind denominator and down both begin with a d, the bottom part of a fraction is the denominator.  Now that you have a decimal, move the decimal point 2 places to the right (you want to know how many hundredths there are) and add the % sign.

To convert from a % to a decimal, reverse the process.  Move the decimal two places to the left and remove the % sign.  To convert it to a fraction put the number over 100 and remove the % sign.  So 38% is the same as 38/100, or .38.

You should spend some time understanding %, if you haven't already.  It keeps popping up in everything from the arts to science.  You also see it whenever you're shopping - 15% off, this week only.

Where did the name come from?

Like so many names, this comes from the latin Per Centum which means 100.  Isn't it a wonder that latin is a dead language but we still use it in to derive so many English words.  We could have used the word hundreds and saved everyone a log of confusion.  Where did we get the word hundred?  The best I could find out seemed to link it to the Old English word hund.

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