If are the means of n groups with number of observations respectively, then the mean of all the groups taken together is

Let be the mean of x₁, x₂, …., x_n and be the mean of y₁, y₂, …y_n. If is the mean of x₁, x₂, …., x_n, y₁, y₂…, y_n, then = ?

If is the mean of x₁, x₂, …, x_n then for a ≠ 0, the mean of

The mean weight of six boys in a group is 48 kg. The individual weights of five of them are 51 kg, 45 kg, 46kg and 44 kg. The weight of the 6^th boy is

The mean of the marks scored by 50 students was found to be 39. Later on it was discovered that a score of 43 was misread as 23. The correct mean is