Q.Calculate Mode : 12, 11, 15, 11, 12, 12, 15, 12, 9, 12

The median is the positional middle value of a series arranged in order — found directly for an individual series (the $(N+1)/2$th item if $N$ is odd, or the average of the two middle items if $N$ is even), via cumulative frequency for a discrete series, and via $Median=l+\frac{(N/2)-cf}{f}\times h$ for a continuous series, using the median class's lower boundary $l$, the cumulative frequency $cf$ of the class before it, its own frequency $f$, and its width $h$. The mode is the most frequently occurring value — found by inspection (or the grouping method, when close frequencies make inspection unreliable) for individual/discrete series, and via $Mode=l+\frac{f_1-f_0}{2f_1-f_0-f_2}\times h$ for a contin …