freshwater rivers and lakes. (see exercise 7.13 for additional details.) for certain species of fish, the lc50 measurements (in parts per million) for ddt in 12 experiments were as follows: 16, 5, 21, 19, 10, 5, 8, 2, 7, 2, 4, 9 estimate the true mean lc50 for ddt with confidence coefficient .90. assume that the lc50 measurements have an approximately normal distribution