Question

If the average marks of three batches of 50, 60 and 70 students respectively is 65, 50 and 80, then the average marks of all the students is:
1. 66
2. 55 
3. 62 
4. 60 

Answer 1

Correct Answer - Option 1 : 66

Given 

Three batches of student = 50, 60, 70 

The average marks of three batches = 65, 50, 80,

Formula Used 

Average = sum of data/No. of data

Calculation 

Sum of marks of 50 student = 50 × 65 = 3250

Sum of marks of 60 student = 60 × 50 = 3000

Sum of marks of 70 student = 70 × 80 = 5600

 Average marks of all students  = Sum of markets obtained by all students/Total number of students

⇒ (3250 + 3000 + 5600)/(50 + 60 + 70)

⇒ 11850/180 = 65.83  = 66(approx.)

∴ The average marks of all students is 66.