 Hello and welcome to the session. Let's work out the following problem. It says the mean of 30 observations was 150. It was detected on checking that one observation of 165 was wrongly copied as 135 for the computation of mean. Find the correct mean. We have to find the correct mean. So let's now move on to the solution. Now we know that the mean is given by the formula sum of all the observations upon the number of observations. X bar is the mean. Summation X is the sum of observation and n is the number of observations. Right? So from this we have sum of the observations is equal to n into mean. So now here n is 30 and mean is given to be 150. So summation x that is sum of the observations is 30 into 150 that is 4500. Right? Now we are given that one observation of 165 was wrongly copied as 135 that means we added 30 less in these sum of the observations. Right? So the correct sum is equal to incorrect sum plus the correct observation minus incorrect observation. Now this is the incorrect sum because in this sum one of the observation of 165 was wrongly copied as 135 that means we need to add 30 more to it because this sum contains one of the observation as 135 in place of 165. So this is 4500 plus correct observation which is 165 minus incorrect observation which is 35135. So this is 4500 plus 30. So this is 4530. So now the correct mean is equal to x bar. Now the sum of the observations is 4530 upon 30 which is equal to 151. So the correct mean is 150 1. So this completes the question and the session. Bye for now. Take care. Have a good day.