SOLUTION: The total annual sales of a book in either paper or electronic form are 3500. Each paper copy of the book costs $30 and each e-book costs $25. The total cost is $97 500. (a) If

Question 1172716: The total annual sales of a book in either paper or electronic form are 3500. Each paper
copy of the book costs $30 and each e-book costs $25. The total cost is $97 500.
(a) If x and y denote the number of copies in paper and electronic form, write down a pair of
simultaneous equations.
(b) Solve the equations to find the number of e-books sold.
Answer by ikleyn(52788) (Show Source): You can put this solution on YOUR website!
.


(a)  A pair of simultaneous equations is


           x +   y = 3500     (1)    (counting the books)

         30x + 25y = 97500    (2)    (counting dollars)



    Writing these equations is absolutely standard and routine step,

    it does not requires any explanations, because everything is clear and obvious as is.



(b)  To find the number of e-books y, express x = 3500-y from equation (1)

     and substitute it into equation (2).  You will get single equation for y


          30*(3500-y) + 25y = 97500


     and from this equation  y =  = 1500.


ANSWER.  1500 e-books were sold.

Solved.

--------------------

This problem is of the same type as the classic tickets problems.

There are different methods of solving such problems. Read the lessons
    - Using systems of equations to solve problems on tickets
    - Three methods for solving standard (typical) problems on tickets
in this site.

From these lessons, learn on how to solve such problems once and for all.

Also, you have this free of charge online textbook in ALGEBRA-I in this site
    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this online textbook under the topic "Systems of two linear equations in two unknowns".

Save the link to this online textbook together with its description

Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson

to your archive and use it when it is needed.

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