interest-earning assets including unearned income in the accretion of fair value adjustments on discounts recognized on acquired or purchased loans is recognized based on the constant effective yield of the financial instrument . the timing and amount of revenue that we recognize in any period is dependent on estimates , judgments , assumptions , and interpretation of contractual terms . changes in these factors can have a significant impact on revenue recognized in any period due to changes in products , market conditions or industry norms . residential and commercial mortgage servicing rights we elect to measure our residential mortgage servicing rights ( msrs ) at fair value . this election was made to be consistent with our risk management strategy to hedge changes in the fair value of these assets as described below . the fair value of residential msrs is estimated by using a cash flow valuation model which calculates the present value of estimated future net servicing cash flows , taking into consideration actual and expected mortgage loan prepayment rates , discount rates , servicing costs , and other economic factors which are determined based on current market conditions . assumptions incorporated into the residential msrs valuation model reflect management 2019s best estimate of factors that a market participant would use in valuing the residential msrs . although sales of residential msrs do occur , residential msrs do not trade in an active market with readily observable prices so the precise terms and conditions of sales are not available . as a benchmark for the reasonableness of its residential msrs fair value , pnc obtains opinions of value from independent parties ( 201cbrokers 201d ) . these brokers provided a range ( +/- 10 bps ) based upon their own discounted cash flow calculations of our portfolio that reflected conditions in the secondary market , and any recently executed servicing transactions . pnc compares its internally-developed residential msrs value to the ranges of values received from the brokers . if our residential msrs fair value falls outside of the brokers 2019 ranges , management will assess whether a valuation adjustment is warranted . for 2011 and 2010 , pnc 2019s residential msrs value has not fallen outside of the brokers 2019 ranges . we consider our residential msrs value to represent a reasonable estimate of fair value . commercial msrs are purchased or originated when loans are sold with servicing retained . commercial msrs do not trade in an active market with readily observable prices so the precise terms and conditions of sales are not available . commercial msrs are initially recorded at fair value and are subsequently accounted for at the lower of amortized cost or fair value . commercial msrs are periodically evaluated for impairment . for purposes of impairment , the commercial mortgage servicing rights are stratified based on asset type , which characterizes the predominant risk of the underlying financial asset . the fair value of commercial msrs is estimated by using an internal valuation model . the model calculates the present value of estimated future net servicing cash flows considering estimates of servicing revenue and costs , discount rates and prepayment speeds . pnc employs risk management strategies designed to protect the value of msrs from changes in interest rates and related market factors . residential msrs values are economically hedged with securities and derivatives , including interest-rate swaps , options , and forward mortgage-backed and futures contracts . as interest rates change , these financial instruments are expected to have changes in fair value negatively correlated to the change in fair value of the hedged residential msrs portfolio . the hedge relationships are actively managed in response to changing market conditions over the life of the residential msrs assets . commercial msrs are economically hedged at a macro level or with specific derivatives to protect against a significant decline in interest rates . selecting appropriate financial instruments to economically hedge residential or commercial msrs requires significant management judgment to assess how mortgage rates and prepayment speeds could affect the future values of msrs . hedging results can frequently be less predictable in the short term , but over longer periods of time are expected to protect the economic value of the msrs . the fair value of residential and commercial msrs and significant inputs to the valuation model as of december 31 , 2011 are shown in the tables below . the expected and actual rates of mortgage loan prepayments are significant factors driving the fair value . management uses a third-party model to estimate future residential loan prepayments and internal proprietary models to estimate future commercial loan prepayments . these models have been refined based on current market conditions . future interest rates are another important factor in the valuation of msrs . management utilizes market implied forward interest rates to estimate the future direction of mortgage and discount rates . the forward rates utilized are derived from the current yield curve for u.s . dollar interest rate swaps and are consistent with pricing of capital markets instruments . changes in the shape and slope of the forward curve in future periods may result in volatility in the fair value estimate . residential mortgage servicing rights dollars in millions december 31 december 31 .

december 31 2011: fair value: 647
weighted-average life ( in years ) ( a ): 3.6
weighted-average constant prepayment rate ( a ): -22.1
weighted-average option adjusted spread: -11.77
december 312010: fair value: 1033
weighted-average life ( in years ) ( a ): 5.8
weighted-average constant prepayment rate ( a ): -12.61
weighted-average option adjusted spread: -12.18

weighted-average constant prepayment rate ( a ) 22.10% ( 22.10 % ) 12.61% ( 12.61 % ) weighted-average option adjusted spread 11.77% ( 11.77 % ) 12.18% ( 12.18 % ) ( a ) changes in weighted-average life and weighted-average constant prepayment rate reflect the cumulative impact of changes in rates , prepayment expectations and model changes . the pnc financial services group , inc . 2013 form 10-k 65 .

Questions:
what was the fair value of residual mortgage rates in 2010?
what was the value in 2011?
what is the sum?
what is the average value per year?

Answers:
1033
647
1680
840