Question 1139187
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<pre>
Let n = # of pigs originally bought.


Then you have this equation from the condition


    {{{(200+72)/(n-4)}}} - {{{200/n}}} = 7,   or


    {{{272/(n-4)}}} - {{{200/n}}} = 7.


Multiply both sides by n*(n-4), simplify and solve for n


    272n - 200*(n-4) = 7n*(n-4)

    72n + 800 = 7n^2 - 28n

    7n^2 - 100n - 800 = 0

    n = {{{(100 +- sqrt(100^2 + 4*7*800))/(2*7)}}} = {{{(100 +- 180)/14}}}.


The solution to the problem is the positive integer  n = {{{(100 + 180)/14}}} = {{{280/14}}} = 20.


<U>ANSWER</U>.  There were 20 pigs originally.


<U>CHECK</U>.    {{{272/16}}} - {{{200/20}}} = 17 - 10 = 7  dollars  profit for each of 16 sold pigs.   ! Correct !
</pre>

Solved.


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