Calculate the Coefficient of Skewness for the given grouped data using two methods.

To calculate the Coefficient of Skewness using two methods, we first need to compute the Mean, Median, Mode, Standard Deviation, and Quartiles from the given grouped data.

Step 1: Create an extended table for calculations.
We assume the class intervals are inclusive (e.g., 40-49, 50-59, etc.) and thus the true class boundaries are 39.5-49.5, 49.5-59.5, etc. The class width ($w$) is 10.

| Marks | True Class Boundaries | Midpoint ($x$) | Frequency ($f$) | $f \cdot x$ | $x^2$ | $f \cdot x^2$ | Cumulative Frequency