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% ( 2.5 % )', '3.2% ( 3.2 % )', '4.4% ( 4.4 % )'], ['expected term ( in years )', '6.17', '6.25', '6.25'], ['expected volatility', '41.7% ( 41.7 % )', '37.9% ( 37.9 % )', '30.9% ( 30.9 % )'], ['expected dividend yield', '0.4% ( 0.4 % )', '0.3% ( 0.3 % )', '0.6% ( 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. .

Question: what is the average expected volatility for the years 2007-2009?
Answer: 36.83%
Explanation: it is the sum of all percentages of expected volatility during this period divided by three .