Areal estate salesperson bought promotional calendars and date books to give to her customers at the end of the year. the calendars cost $0.40 each, and the date book cost $0.75 each. she ordered a total of 300 promotional items and spent $190. how many of each item did she order?

You have to solve two equations simultaneously.  The equations are:
.40c + .75d =$190
     c +  d  = 300.
Multiply this second equation by -0.4 on both sides leaving you -0.40c -0.40d = 120.  Subtract this new equation from the first and solve for d.
  0.40c + 0.75d = 190
- 0.40c - 0.40d = 120

            0.35d = 70
    Solve for d.  70/0.35d  d = 200.  Plug this number back into the original equation and c = 100.

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