In calculating the mean of grouped data,grouped in classes of equal width,we may use the formula $\bar{x} = a + \frac{\sum f_i d_i}{\sum f_i}$,where $a$ is the assumed mean. $a$ must be one of the mid-points of the classes. Is the last statement correct? Justify your answer.

(N/A) No,the statement is incorrect. While it is common practice to choose the assumed mean $a$ as one of the class marks (mid-points) to simplify calculations,it is not a mathematical requirement. The assumed mean $a$ can be any arbitrary value chosen from the data set or even outside it,provided it helps in simplifying the calculation of deviations $d_i = x_i - a$.