If the average marks of three batches of 55, 60 and 45 students respectively is 50, 55, 60, then the average marks of all the students is _____ ?

55 students get average marks of 55%.
so 55*50=2750
similarly 60*55=3300
& 60*45=2700
now total no of marks obtain by all students of three batches= 2750+3300+2700=8750/=
Total no of students= 55+60+45=160.
By dividing total marks on each student , we get average marks obtain by each student
so 8750/160 = 54.68