A card is drawn from a deck of $52$ cards. The event $E$ is that card is not an ace of hearts. The number of outcomes favourable to $E$ is

A school has five houses $A, B, C, D$ and $E.$ A class has $23$students, $4$from house $A,$ $8$ from house $B,$ $5$ from house $C,$ $2$ from house $D$ and rest from house $E.$ A single student is selected at random to be the class monitor. The probability that the selected student is not from $A, B$ and $C$ is

In calculating the mean of grouped data, grouped in classes of equal width, we may use the formula,

$\overline{x}=a+\frac{\sum f_i{d}_i}{\sum f_i}$

Where, $a$ is the assumed mean, $a$ must be one of the mid-point of the classes. Is the last statement correct? Justify your answer.