Days of leave taken in a year by 50 employees of a Ranchi office. Note that the class widths are NOT equal:
0-5: 12, 5-10: 14, 10-20: 10, 20-40: 8, 40-60: 6.
Find the mean number of days of leave.

Unequal widths do not change how a class mark is found: 2.5, 7.5, 15, 30, 50. $\sum f_i{x}_i=30+105+150+240+300=825$ and $\sum f_i=50$, so the mean is $\frac{825}{50}=16.5$ days. (Step-deviation cannot be used here — there is no single h.) "21.6" uses the upper limits as $x_i$; "11.4" uses the lower limits; "165" divides by 5, the number of classes.