In an attempt to be environmentally friendly, the city council decides that there must at least 18 trees on each block in thr city. A sample of 20 blocks was randomly surveyed, with these results (numbers of tree per blocks) 24, 17, 7 20 28 27 10 21 30 8 30 27 22 27 27 13 27 20 24 17 what is the sample mean number of trees per block