Question

The mean marks obtained by a class of 40 students is 65. The mean marks of half of the students is found to be 45. The mean marks of the remaining students is

Answer 1

average(mean) = sum/total
mean of 40 students=65
65=sum/40 =sum of 40 members=2600
mean of 20 students=45
45=sum/20=sum of 20 members=900
sum of remaining 20 members= sum of 40 members - sum of 20 members
= 2600-900=1700
so sum of remaining 20 members=1700
mean= sum/total
mean=1700/20=85

Answer 2

Answer:

The mean marks of the remaining 20 students = 85

Step-by-step explanation:

Given,

The mean marks of 40 students in a class  =65

The mean marks of half of the students = 45

To find,

The mean marks of the remaining students

Recall the formula

Mean = $\frac{Sum\ of \ observations}{Total \ no \ of \ observations}$

Solution:

Given, that the mean marks of 40 students in a class  =65

Then we have

65 = $\frac{Total \ marks \ of \ 40\ students}{40}$

∴Total marks of 40 students = 40 ×65 = 2600

Also given, the mean marks of half of the students = 45

Then we have,

45 = $\frac{Total \ marks \ of \ 20\ students}{20}$

∴Total marks of 20 students  = 45 ×20 = 900

Total marks of the remaining 20 students  = 2600 - 900 = 1700

∴ The mean marks of the remaining 20 students = $\frac{1700}{20}$ = 85

The mean marks of the remaining 20 students = 85

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