If the average marks of three batches of 55, 60 and 45 students respectively is 30, 55, 60, then the average marks of all the students is: Choose the correct choice.
A) 53.33  B) 54.68  C) 55  D) 47.81  E) None of these
Explanation:   Required average = (55 × 30 + 60 × 55 + 45 × 60/55 + 60 + 45)   = (1650 + 3300 + 2700/160)   = 7650/160   = 47.81   Answer: 47.81
<result>D</result>
If the average marks of three batches of 55, 60 and 45 students respectively is 30, 55, 60, then the average marks of all the students is: