Natural water contains a small amount of tritium `(`_1^3H)`. This isotope beta -decays with a half-life of 12.5 years.A mountaineer while climbing towards a difficult peak finds debris of some earlier unsuccessful attempt.Among other things he finds a sealed bottle of whisky.On returm he analyses the whisky and finds that it contains only 1.5 per cent of hte ``_1^3H` radioactivity as compared to a recently purchased bottle marked '8 years old' .Estimate the time of that unsuccessful attempt.