The number of students absent in a class were recorded every day

Let the assume mean be $A=4$.

We know that mean, $\bar{X}=A+\frac{1}{N} \sum_{i=1}^{n} f_{i} d_{i}$

Now, we have $N=\sum f_{i}=120, \sum f_{i} d_{i}=-57$ and $A=4$.

Putting the values in the above formula,

$\bar{X}=A+\frac{1}{N} \sum_{i=1}^{n} f_{i} d_{i}$

$=4+\frac{1}{120} \times(-57)$

$=4-\frac{57}{120}$

$=4-0.475$

$=3.525$

$\approx 3.53$ (approximate)

Hence, the mean number of students absent per day is approximately 3.53.