Find the mean number of mangoes kept in a packing box. Which method did you choose?

The class mark is the midpoint of the class interval.
For 50 - 52: $x_1 = \frac{50+52}{2} = 51$
For 53 - 55: $x_2 = \frac{53+55}{2} = 54$
For 56 - 58: $x_3 = \frac{56+58}{2} = 57$
For 59 - 61: $x_4 = \frac{59+61}{2} = 60$
For 62 - 64: $x_5 = \frac{62+64}{2} = 63$

Let's choose the middle class mark as the assumed mean, $A = 57$.
The class size $h$ is the difference between consecutive class marks, $h = 54 - 51 = 3$.

We can organize these calculations in a table:

The formula for the mean ($\bar{x}$) using the step-deviation method is:

Substitute the values:

The method chosen is the Step-Deviation Method.

The mean number of mangoes kept in a packing box is $\text{57.1875 mangoes}$.