Everybody who has ever attended a High School knows
what an equation is. Don't think, however, that because you
learn about equations in high school, that a high school education
is necessary before you can understand equations.
    
Because they are part of the Radio-Trician's language, we
must know, not only what they are but how to use them. All
of this can be explained in a few words.
    
Going back to the dealer who gave the factory details about
his business--he may have said something about the profit he
was able to make on each sale. Suppose he said something like
this: "I have cut my operating costs, I have my business well
in hand, my profit is actually one-fourth of my sales."
    
So for each dollar he takes in, 25 cents is profit and goes
right into his pocket. This is a simple statement and easy to
grasp, but suppose the manufacturer is interested in knowing
the exact profit of the dealer for each year he was in business.
    
He has this statement to begin with--"profit is one-quarter
sales." But he is a busy man--he doesn't want to write any
unnecessary words. So he can reduce the statement--instead
of writing out the words for profit and sales, he can take just
the first letter of each as symbols. Then the statement would
be--p is 1/4 s. But "is" means "equals." He knows the symbol
for the word "equals," which is "=." Now he writes the
statement in this form-- p=l/4s
or p = s/4
    
This is the original statement reduced to its shortest possible
form. And this is an equation (the word equation means--
"has been made equal").
    
Using this equation, the manufacturer can easily calculate
the profit on a sale of any size. If it is known that the total
sales the first year our dealer was in business amounted to
8000 dollars, can we find his profit? Easily enough. Take the
original statement in equation form and instead of "s" put in
8000. Ther) it will appear in this form p = 8000/4. Then all we
have to do is divide 8000 by 4 which is 2000. So p or profit is
2000 dollars.
    
We can do the same thing for every week the dealer was in
business, knowing the amount of money he took in from sales