Brihat Parashara Hora Shastra
अर्द्धमर्धं तु शेषाणां ह्येतत् स्वीयमुदाहृतम्। पूर्णं विंशोपकं विंशो धृतिः स्यादधिमित्रके॥ २४॥
and the rest of the nine divisions each a half. The Vimshopak Bal remains as 20, only when the Grah is in own Bhava Vargas.
english translation
arddhamardhaM tu zeSANAM hyetat svIyamudAhRtam। pUrNaM viMzopakaM viMzo dhRtiH syAdadhimitrake॥ 24॥
hk transliteration by Sanscript