def find_index_of_minimum(arr):
    """Returns the index of the minimum number

    Arguments:
        arr {list} -- the input list

    Returns:
        int -- the index of the minimum number
    """
    minimum = arr[0]
    index_of_minimum = 0

    for index, item in enumerate(arr):
        if item < minimum:
            minimum = item
            index_of_minimum = index

    return index_of_minimum