def part2(all_groups_answer):
    """ count questions answered 'yes' by everyone """
    everyone_answered = 0
    for group_answers in all_groups_answer:
        answered = set("abcdefghijklmnopqrstuvwxyz")
        for answer in group_answers:
            # answered = answered.intersection(set(answer))
            answered.intersection_update(set(answer))

        everyone_answered += len(answered)

    return everyone_answered