You need to order the data, so 11, 12, 13, 14, 14, 15, 17, 17, 18, 18, 18, 20 Then find the middle of the data. Because there are 12 data points, the median will lie between the two 6th placed numbers The two numbers are 15 and 17, so work out the mean of them. (15+17)/2 = 16 So the answer is B. 16
