AP Calculus AB
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A river boat company offers a 4th of july trip to an organization with understanding that there will be at least 400 passengers. each ticket is $12, and company agrees to refund $.20 to every passenger for each 10 passengers in excess of 400. find the number of passengers that makes the total revenue a maximum.

revenue = price * tickets
If 400+x tickets are sold,
r = (12  .2x/10)(400+x)
r reaches max at x=100, or 500 tickets sold 
A piece of wire of length 246cm is cut into 12 parts whose length are in an A.P. Given that the sum of four shortest parts is 34cm, find the length of the longest part.