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

What is the class-mark of class 25-35?

If the classes are 0-10, 10-20, 20-30... then in which class should the observation 10be included?

The mean of five numbers is 80, out of which mean of 4 numbers is 46, find the 5th number :

Mean of 100 observations is 40. The 9th observation is 30. If this is replaced by70 keeping all other observations same, find the new mean.