A group of 210 students appeared in some test. The mean of 3rd of stud

1.	A group of 210 students appeared in some test. The mean of 3rd of students is found to be60. The mean of the remaining students is found to be 78. The mean of the whole group willbe:(1) 74(2) 72(3) 80(4) 76
Answer» Total students = 210 1/3 rd of 210 = 70 students Mean marks of 70 students = 60 Let the sum of marks of 70 students be x Mean = x/Number of students 60 = x/70 x = 7060 ⇒ Sum of marks of 70 students= 4200 Remaining students = 210 - 70 = 140 students Mean of 140 students = 78 Sum of marks of 78 students = 14078 = 10920 Total marks of 210 students = 4200 + 10920 = 15120 Mean of whole group = 15120/210 = 72 marks

A group of 210 students appeared in some test. The mean of 3rd of students is found to be60. The mean of the remaining students is found to be 78. The mean of the whole group willbe:(1) 74(2) 72(3) 80(4) 76

Answer»

Total students = 210

1/3 rd of 210 = 70 students

Mean marks of 70 students = 60

Let the sum of marks of 70 students be x

Mean = x/Number of students

60 = x/70

x = 70*60

⇒ Sum of marks of 70 students= 4200

Remaining students = 210 - 70 = 140 students

Mean of 140 students = 78

Sum of marks of 78 students = 140*78 = 10920

Total marks of 210 students = 4200 + 10920

= 15120

Mean of whole group = 15120/210

= 72 marks