def average_fixxations_time(fixxations_times):
    """

    :param fixxations_times:  a list of tuples with (start_time_inclusive, end_time_exclusive)
    :return:                returns the average time of fixxations
    """

    return sum([fixxation_time[1] - fixxation_time[0] for fixxation_time in fixxations_times]) / len(fixxations_times)