輕鐵還有二十元一天票?

你可以在各西鐵線車站的服務台購買:
屯門 -- 南昌全日通 (@$20./日票)
憑票當日無限次數往來: 屯門站至南昌站
若由南昌站往柯士甸站, 尖東站或紅磡站, 則要另外購車票.
憑屯門-南昌全日通: 可免費轉乘輕鐵,
但轉乘巴士 K16 則要付車費 (@4.40).

Yes,West Rail line day pass can takeMTR West Rail line,light rail and MTR bus in that day freedomly.This day pass is costs $20 per each and it will sell at West Rail line Customer service center(expect Austin,East Tsim Sha Tsui and Hung Hom Station)
Day Pass information:http://www.mtr.com.hk/chi/whatsnew/images/monthly_day_pass.pdf
Hope above information can help you!

西鐵全日通可在各西鐵線車站買得到

yes, you can go to the service center in any MTR center to get one for that day. It can be used for riding the buses provided by MTR for free too!!