Median is always the middle number of the set of data, so lets re order the numbers least to greatest
1,2,4,5,6,7,8,8,9,12
Since there's an even amount there wont be an exact middle number, however we know its in-between 6 and 7. So we can do 6+7 = 13 and then 13/2 = 6.5 to get the middle number or median.
