The mean of 25 observations is 27. If one observation is included, the mean still remains 27. Find the included observation.

The mean of 5 observations is 15. If the mean of first three observations is 14 and that of the last three is 17, find the third observation.

The mean weight of 8 students is 45.5 kg. Two more students having weights 41.7 kg and 53.3 kg join the group. What is the new mean weight?

Mean of 9 observations was found to be 35. Later on, it was detected that an observation 81 was misread as 18. Find the correct mean of the observations.