Mary earns a monthly income of $3,000. She spends the entire amount each month at the rate of $100 a day. (Assume there are 30 days in the month.)...

Mary earns a monthly income of $3,000. She spends the entire amount each month at the rate of $100 a day. (Assume there are 30 days in the month.) The interest rate paid on bonds is 5% per month. It costs $10 every time Mary sells a bond.

(a) Describe briefly how Mary should go about deciding how much money to hold.

ANS:

(b) Mary can switch from bonds to cash up to a maximum of three times. How many times should Mary switch from bonds to cash?