Question 114792
Life as a boy + Life as young man + Life as adult + Life in old age=Whole life
{{{1/4+1/5+1/3+O=1}}}
Where O is the fraction of his life spent in old age. 
{{{60*(1/4+1/5+1/3+O)=60}}} Multiply both sides by 60 (4*5*3) to remove fractions.
{{{15+12+20+60(O)=60}}}
{{{60(0)=13}}}
{{{O=13/60}}}
The man spent 13/60 of his life in old age. 
His total years in old age equals 13 years. 
{{{(13/60)A=13}}}
{{{A=60}}}
The man was 60 years old when he died.