I was distracted by 9gag yesterday, and I saw this riddle by Einstein. It was said that only 2% of people who tried can answer it, but I think, what was really meant by that is; there are only 2% of people who tried answering it without making notes can be successful.....or, something like that.
I've tried making notes, but it was quite hard for me. So, I developed a method in answering it. It might not be new to others, but I just thought of it to make the riddle a lot easier. I solved it in 10 minutes or so.
So, why don't you give it a go?