100%- 5%= 95% so the value is multiplied by .95 every year. If the original value is V, the value after n years is so you need to solve . The "P" cancel and taking logarithms of both sides, x log 0.95= log 0.5 so x= (log 0.95)/(log 0.5).

If inflation is 5%, then the "real" devaluation is 10%. The value of a house is multiplied by 1.00- .10= .90 each year.