The mean of 50 observations was 250. later it was found that the number 152 was wrongly copied as 102 for the computation of means. find the correct mean.

Dear student, 
Here, we have
No. of observation, N = 50 
Incorrect Mean = 250 
Right item = 152 
Wrong item = 102 
 
As we know that 
 
Mean = Sum of observation ( X )/ No. of observation
 
250 = X /50 
 
X = 12,500 
 
Hence sum of observation is 12,500 
 
Now 
 
Correct sum of observation = 12500 - Wrong item + Correct item 
 
= 12500 - 102 + 152 
= 12, 550
 
 
Now correct Mean 
 
Mean = 12550/ 50 
= 251 
 
Hence the correct Mean = 251

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