Question 1190398
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The cinema sells boxes of popcorn in two sizes: small and large. A small popcorn
costs $5.50, and a large popcorn costs $7.50. If 300 boxes of popcorn were sold for a
total of $3517.50, how many of each size popcorn were sold?
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The numbers in your post describe  IMPOSSIBLE  situation,  which  NEVER  may happen.


Indeed,  the numbers of different types of boxes are  EITHER  both even  OR  both odd

(since their sum is the even number  300,  it  CAN  NOT  be in different way).



If the numbers of different types of boxes are both even integer numbers, 
then the total revenue must be integer number of dollars.


If the numbers of different types of boxes are both odd integer numbers, 
then the total revenue must be integer number of dollars,  again.


With the revenue  $3517.50 pointed in your post,  the problem is  DEFECTIVE  and can not be solved in integer numbers.