# 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. ## Converting

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.

III. Algebra

VI  Equations

VII. Exponents

IX Fractions

XIII.  Linear Equations

XVII.  Real Numbers

XIV.  Math Terms

XVIII.  Percentages

XV.  Matrices

XIX.  PEMDAS Order of Operations

XXII. Slope

XXIII,  Quadratics

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