arithmetic of currency futures and libor-rate arbitrage

http://www.forbes.com/global/2009/0608/foreign-exchange-devaluation-buy-junky-currencies.html

If the one-year Libor (bank lending rate) is 2% for U.S. dollar borrowings but 3% for the Danish krone, there's going to be a built-in deterioration in the value of kroner in the futures market. Say that the spot value of a krone is 18 cents. Then the futures value one year out should be 17.82 cents, or 1% less. Why? If the June 2010 krone future were any higher than 17.82 cents, banks could lock in profits by borrowing dollars at 2% and lending kroner at 3%, while erasing their currency exposure by selling kroner futures.

yen-dollar carry trade

http://www.forbes.com/global/2009/0608/foreign-exchange-devaluation-buy-junky-currencies.html

This, essentially, is the currency arbitrage strategy known as the carry trade:
You decide to borrow Japanese yen, exchange them for dollars and stick the proceeds into one-year U.S. Treasurys.

The yen cost you less than 1% to borrow, while Treasurys are paying more than 5%. Since banks require you to put down only 20%, the four-percentage-point interest rate spread earns you a 20% annual profit. Bear markets, bankruptcies and changes in governments don't bother you. The only thing that can go wrong is if your dollars fall in value against the yen that you must repay.

....in last fall's financial crisis the dollar plunged against the yen, ruining that carry trade.