A group of 210 students appeared in some test. the mean of 13 rd of students is found to be 60. the mean of the remaining students is found to be 78. the mean of the whole group willbe :
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Solution :-
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
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
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Answer:
72 marks...............
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