The compensation expenses were determined by calculating the fair value of each option grant using  the Black-Scholes option-pricing model. SENAO used the following weighted-average assumptions in  calculating the fair value of the options granted:  Risk-free interest rate is based on the rate of the Taiwan government bonds in effect at the time of grant.  Expected volatilities are based on historical volatilities of stock prices of the similar company in the same  industry and SENAO. Expected life represents the periods that SENAO’s share-based awards are expected  to be outstanding and was determined based on historical experience regarding similar awards, giving  consideration to the contractual term of the share-based awards. The dividend yield is zero as share-based  awards agreeing on that the price will be adjusted when SENAO pays dividends, with the exception of  the options granted in 2007. The expected dividend yield for SENAO’s 2007 Plan is based on anticipated  future cash dividends yield at the time of grant.  c. Marketable securities  F-75 Year Ended  December 31, 2010 Expected dividend yield 0-1.49% Expected volatility 39.63-53.07% Risk free interest rate 1.75-2.00% Expected life 4.375 years December 31, 2009 Carrying  Amount Unrealized  Gain Unrealized  Loss NT$ NT$ NT$ (In Millions) Available-for-sale securities Open-end mutual funds $  16,832  $  90  $  552  Domestic listed stocks 500  28  4  Corporate bonds 103  1  —  Real estate investment trust fund 102  7  9  17,537  126  565  Held-to-maturity securities Corporate bond 4,532  1  39  Bank debentures 498  3  1  5,030  4  40  $  22,567  $  130  $  605 