The average marks of 30 students is 65, 36 students is 35 and 34 students is 45. The average marks for all the students is:

45.3 46.4 45.7 47.4

47.4

Sum of marks of 30 students = 30 × 65 = 1950 Sum of marks of 36 students = 36 × 35 = 1260 Sum of marks of 34 students = 34 × 45 = 1530 Average of all = \(\frac{1950 + 1260 +  1540 }{30 + 36 + 34 }\) = \(\frac{4740}{100}\) = 47.4