Brihat Parashara Hora Shastra
मध्ये योगत्रयेणैवं खाष्टतुल्याब्दकाः स्मृताः । द्व्यगा योगद्वयेनाऽत्रयोगैकेनाब्धिषण्मिताः ॥ ४२॥
If medium life is arrived at by three groups, it is 80 years, if indicated by 2 groups, it is 72 years and, if by one group, it is 64 years.
english translation
madhye yogatrayeNaivaM khASTatulyAbdakAH smRtAH । dvyagA yogadvayenA'trayogaikenAbdhiSaNmitAH ॥ 42॥
hk transliteration by Sanscript