Question 1154401
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The math department bought some calculators for a {{{highlight(cross(lot))}}} <U>total</U> of $240 . 
The department head kept one for the math office and then sold the rest for $300 making a profit of $5 
on each calculator. How many calculators did the math department buy ?
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Let n be the number of calculators the department bought.


Then it sold (n-1) calculator.


The buying price for each single calculator was {{{240/n}}}.

The selling price was  {{{300/(n-1)}}}.

The difference in prices was 5 dollars


    {{{300/(n-1)}}} - {{{240/n}}}  = 5   dollars.


Simplify dividing by 5 both sides


    {{{60/(n-1)}}} - {{{48/n}}} = 1


Multiply both sides by n*(n-1)


    60n - 48*(n-1) = n*(n-1)

    60n - 48n - 48 = n^2 - n

    n^2 - 13n - 48 = 0

    (n-16)*(n+3) = 0


Of two roots, 16 and -3, only positive n= 16 is meaningful.


<U>ANSWER</U>.  16 calculators were bought.
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