Question

the mean of 20 observation is 31 later on it was detected that an observation was taken as 52 instead of 25 find the correct mean

Answer 1

Let Observations be x1,x2,.........................x20

We are given, x1+x2+.............+x20/20 = 31
           so, x1+x2+.................x20 = 620

Let incorrect observation be x20

 so, x1+x2+x3+..........x19 + 52 = 620
      so, x1+x2+x3...............x19 = 568
    
Correct mean = x1+x2+x3+..............x19 + 25/20
                       = 568 + 25/20 
                       = 29.65

Hence, Correct mean is 29.65