input: Write a python function to determine if a number is even or odd.
  assert is_even_odd(4) == "even"
  assert is_even_odd(7) == "odd"
  assert is_even_odd(10) == "even"
  assert is_even_odd(15) == "odd"
output: def is_even_odd(n):
      return "even" if n % 2 == 0 else "odd"