Question

If you want to earn 15% annual simple interest on an investment, how much should you pay for a note that will be worth $27,000 in 10 months?

Answer 1

For some payment P, you want
  27000 = P + I
  27000 = P + Prt . . . . substituting the formula for I
  27000 = P(1 + .15·10/12) = 1.125
Then
  27000/1.125 = P = 24000

You should pay $24,000 for the note.