These are actually pretty easy to make and work very well. I'd suggest checking out the site and giving one a go. I know I spent more time walking back and fourth than I'd care to admit.
Three guests check into a hotel room. The clerk says the bill is $30, so each guest pays $10. Later the clerk realizes the bill should only be $25. To rectify this, he gives the bellhop $5 to return to the guests. On the way to the room, the bellhop realizes that he cannot divide the money equally. As the guests didn't know the total of the revised bill, the bellhop decides to just give each guest $1 and keep $2 for himself. Each guest got $1 back: so now each guest only paid $9; bringing the total paid to $27. The bellhop has $2. And $27 + $2 = $29 so, if the guests originally handed over $30, what happened to the remaining $1?
$25 for the bill, $2 for the bellhop, and $3 back to the customers. It's a trick, so "$27+$2=$29" is wrong math as the $27 is already the total paid, $2 is the money the bellhop took which is already part of the $27, meaning the $29 is meaningless.
Because the math is wrong. When he gives each guy a dollar back, that's three, not two. 25+3=28, not 25+3=27. With the clerk taking the two dollars, he bring back the total to 30 in all. Easy concept.
its not counting back up at that point, it needs to subtract. Once all of them has paid it is $27, with the -$2 of the bellhop, you get $25 paid for the room.
I've finally figured this one out. The ballerina changes the leg she stands on from time to time, but she does it at a time where you don't see the transition.
Try to look at what leg she holds up, and you'll see that it changes.
If you look at the left ballerina they will all spin right, but if you look at the right ballerina they will all spin left. I don't know the science behind it, but it's something to do with how your brain perceives things and what side of the brain you use.
Well, the last time I saw this - when it was only one lady and not three, the point of it was to, as you say, see which side of your brain you use. If you used one side it spun clockwise, and the other counter-clockwise. Me and my brother saw it spinning opposite directions.
If you focus on the middle one, you can get them all to look like they're spinning in the same direction. You can see it out of the corners of your eyes.