Tickets for the father-and-son breakfast were $2.00 for fathers and $1.50 for sons. If a total of 75 tickets were sold for 127.50, how many fathers and how many sons attended the breakfast?

Let f represent the number of tickets for fathers. The total revenue equation is
  2.00*f + 1.50*(75-f) = 127.50
  .50*f + 112.50 = 127.50    (use the distributive property, collect terms)
  .50*f = 15.00    (subtract 112.50)
  f = 30    (multiply by 2)

30 tickets were sold for fathers and 45 tickets were sold for sons. There is not enough information to tell how many attended breakfast.