At the start of the year a company wants to invest excess cash in one-month, three-month and six-month CD's. The company is somewhat conservative and wants to make sure it has a safety margin of cash on hand each month. (left over from previous month/ available at the outset, plus principal and interest from CD's that have become due, minus investments made at the start of the month, must be no less than the safety margin.)

These are the safety margins:

Jan       $175,000

Feb      $90,000

Mar      $80,000

Apr      $180,000

May     $150,000

June     $85,000

How should it maximize total earned interest? Given that Three-month CD's can only be bought in Jan and April; six-month CD's can only be bought in January.

Initial cash available is 400,000

1-mo CD's      1.0%    1          $2,000             Jan thru June

2-mo CD's      4.0%    3          $3,000             Jan and April

3-mo CD's      9.0%    6          $5,000             Jan

What are the decision variables and the object function?

Define cash flow constraints