Wrong move:

Using mode for grouped data by picking the highest frequency class midpoint

Why:

The modal class is the group with highest frequency, and an estimated mode requires interpolation not just the midpoint value

Correct move:

Identify the modal class first, only use interpolation if explicitly asked for an estimated mode value

Wrong move:

Calculating mean for grouped data using raw class limits instead of midpoints

Why:

Grouped data uses midpoints as a representative value for all observations in the class interval

Correct move:

Multiply each class midpoint by its frequency, sum the products, then divide by total frequency to find the grouped mean

Wrong move:

Using frequency instead of frequency density for histograms with unequal class widths

Why:

Histogram area represents frequency, so unequal widths require density scaling to avoid misleading comparisons

Correct move:

Calculate frequency density = frequency / class width for each interval before plotting a histogram with unequal classes