def to_string(recipe, num_servings):
    """ Return a list of strings with a description of this recipe.

        The recipe will be customized for the given number of servings.
    """
    s = []
    s.append("Recipe for {}, {} servings:".format(recipe['name'],
                                                  num_servings))
    s.append("")
    s.append("Ingredients:")
    s.append("")
    for ingredient in recipe['ingredients']:
        s.append("    {} - {} {}".format(ingredient['ingredient'],
                                         ingredient['amount'] * num_servings /
                                         recipe['num_servings'],
                                         ingredient['units']))
    s.append("")
    s.append("Instructions:")
    s.append("")
    for i,instruction in enumerate(recipe['instructions']):
        s.append("{}. {}".format(i+1, instruction))

    return s