In a retail market, fruit vendors were selling mangoes kept in packing boxes.

The given series is an inclusive series. Firstly, make it an exclusive series.

Let the assumed mean be A = 57 and h = 3.

We know that mean, $\bar{X}=A+h\left(\frac{1}{N} \sum f_{i} u_{i}\right)$

Now, we have $N=\sum f_{i}=400, \sum f_{i} u_{i}=25, h=3$ and $A=57$.

Putting the values in the above formula, we have

$\bar{X}=A+h\left(\frac{1}{N} \sum f_{i} u_{i}\right)$

$=57+3\left(\frac{1}{400} \times(25)\right)$

$=57+\frac{75}{400}$

$=57+0.187$

$=57.187$

Hence, the mean is approximately $57.19$.