input: Write a function to determine the median among three given numbers.
  assert find_median(25, 55, 65) == 55.0
  assert find_median(20, 10, 30) == 20.0
  assert find_median(15, 45, 75) == 45.0
output: def find_median(a, b, c):
      return sorted([a, b, c])[1]