BTIS - Bangalore Transport Information System
is very good site...just enter the source and destination and you will get the bus number. I did not get a bus straight from Majestic to Yeswanthpur so gave you the link..
It would be better if you go to the help desk in Majestic bus stand and ask them. They are really helpful people whether you know Kannada or not (I am from MP, living in B'lore for past 5 years and never felt any discrimination on basis of language)
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