Explanation:
10
The mean of 9, 10, 15, x, 6, 8 and 12 is 11
\(\therefore\text{Mean}=\frac{\text{Sum of observations}}{\text{Number of observations}}\)
\(\Rightarrow11=\frac{9+10+15+\text{x}+6+8+12}{7}\)
\(\Rightarrow\text{x}+60=77\)
\(\Rightarrow\text{x}=77-60=17\)
So, the observations are 9, 10, 15, 17, 6, 8 and 12
Arranging the the observations in increasing order, we get
9, 10, 15, 17, 6, 8, 12 or 6, 8, 9, 10, 12, 15, 17
Thus, the median is 10
Hence, the correct option is (b).