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Q.

The average marks of 10 students in a class was 60 with a standard deviation 4, while the average marks of other ten students is 40 with a standard deviation 6. If all the 20 students are taken together, their deviation will be

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a

96

b

106

c

126

d

5

answer is D.

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Detailed Solution

 n1=10,n2=10
Average  m1=60 m2=40
σ1=4;σ2= to
 Standard deviation of Combined series σ=n1σ12+n2σ22n1+n2+m1n2(m1−m2)2(n1+n2)2=126
 

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