what is the variation observed in the risk-free rate of return during 2008 and 2009?
mastercard incorporated notes to consolidated financial statements 2014 ( continued ) ( in thousands , except percent and per share data ) upon termination of employment , excluding retirement , all of a participant 2019s unvested awards are forfeited . however , when a participant terminates employment due to retirement , the participant generally retains all of their awards without providing additional service to the company . eligible retirement is dependent upon age and years of service , as follows : age 55 with ten years of service , age 60 with five years of service and age 65 with two years of service . compensation expense is recognized over the shorter of the vesting periods stated in the ltip , or the date the individual becomes eligible to retire . there are 11550 shares of class a common stock reserved for equity awards under the ltip . although the ltip permits the issuance of shares of class b common stock , no such shares have been reserved for issuance . shares issued as a result of option exercises and the conversions of rsus are expected to be funded with the issuance of new shares of class a common stock . stock options the fair value of each option is estimated on the date of grant using a black-scholes option pricing model . the following table presents the weighted-average assumptions used in the valuation and the resulting weighted- average fair value per option granted for the years ended december 31: .

|  | 2009 | 2008 | 2007 |
| :--- | :--- | :--- | :--- |
| Risk-free rate of return | 2.5% | 3.2% | 4.4% |
| Expected term (in years) | 6.17 | 6.25 | 6.25 |
| Expected volatility | 41.7% | 37.9% | 30.9% |
| Expected dividend yield | 0.4% | 0.3% | 0.6% |
| Weighted-average fair value per option granted | $71.03 | $78.54 | $41.03 |

the risk-free rate of return was based on the u.s . treasury yield curve in effect on the date of grant . the company utilizes the simplified method for calculating the expected term of the option based on the vesting terms and the contractual life of the option . the expected volatility for options granted during 2009 was based on the average of the implied volatility of mastercard and a blend of the historical volatility of mastercard and the historical volatility of a group of companies that management believes is generally comparable to mastercard . the expected volatility for options granted during 2008 was based on the average of the implied volatility of mastercard and the historical volatility of a group of companies that management believes is generally comparable to mastercard . as the company did not have sufficient publicly traded stock data historically , the expected volatility for options granted during 2007 was primarily based on the average of the historical and implied volatility of a group of companies that management believed was generally comparable to mastercard . the expected dividend yields were based on the company 2019s expected annual dividend rate on the date of grant. .

risk_free_rate_2009 = 0.032
risk_free_rate_2008 = 0.025
risk_free_rate_change = risk_free_rate_2009 - risk_free_rate_2008
answer = risk_free_rate_change * 100