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math's youth lasted 1/6 of his life
he had first beard in the next 1/12th of his life
at the end of the following 1/7th of his life, math got married
5 years from then his son was born
his son live exactly half of maths life
math died four years after the death of his son
how long did math live?
Suppose he lived to be N years old.
From his birth until the end of his youth was N/6 years
From the end of his youth until he grew his first beard was N/12 years.
From the time he shaved off his first beard till he got married was N/7 years.
From the time he got married until his son was born was 5 years.
From the time his son was born until his son died was N/2 years
From the time his son died until he died was 4 years.
All that adds up to N
Multiply through by the LCD = 84
He lived 84 years.