This is really interesting what she did. It's very important. She randomized the 50 workdays. It's important she did this instead of just kind of waking up in the morning and just deciding on her own which bus to take because humans are infamously bad at being random. Even when we think we're being random, we're actually not that random. She might inadvertently be taking bus A earlier in the week where maybe the commute times are shorter, or maybe she inadvertently takes bus A when the weather is better, when there's less traffic. Remember, there's a natural tendency for human beings to want to confirm their hypothesis.