We can’t stop watching this video of a crazy swimming pool stunt. A whole bunch of swimmers stand on each other’s shoulders in a tall, thin line, then the whole stack of people tips over at once into a giant swimming pool. The guy on the bottom doesn’t have to fall very far, but the guy on top hits it hard! The only problem is…the video probably isn’t real! Olympic pools are over 160 feet long, but the falling stack of 20 guys stretches the whole length of the pool. That would make every guy at least 8 feet tall. Also, the tallest human stack ever is only 8 people tall, so 20 probably wouldn’t work. But if someone could do this stunt for real, we’d love to see it!

*Wee ones:* How tall are you in feet, and is that taller or shorter than 8 feet? Find out!

*Little kids:* If the bottom guy and every other guy after that (3rd, 5th, etc.) wore a polka-dot suit and the rest wore plain, what type of suit would the 8th guy be wearing? *Bonus:* If 20 guys stand in a stack, how many swimmers does the very bottom guy have to hold up?

*Big kids:* If every person is 6 feet tall, but everyone’s shoulders are 1 foot shorter than that, how high off the ground would the top of the 3rd guy’s head be? *Bonus:* How high would the top of the 20th guy’s head be?

*The sky’s the limit:* If a tower of 12 people dives, then a tower of 11, then a tower of 10, and so on down to 1 guy tipping over, how many total divers dive? (Shortcut hint: How many people are in the tallest and shortest tower together…then how many in the 2nd tallest and 2nd shortest together…)

Answers:

*Wee ones:* You are shorter…take your height in feet, and see if it’s more or less than 8.

*Little kids:* A plain suit, like all the even-numbered guys. *Bonus:* 19 swimmers.

*Big kids:* 16 feet. The 2nd guy’s feet would stand 5 feet high off the ground, making his shoulders 10 feet high…and then the 3rd guy would be 6 feet tall in total. *Bonus:* 101 feet. The 20th guy’s feet would be 19×5 feet high, or 95 feet, and then he’d be 6 feet tall above that.

*The sky’s the limit:* 78 people. This is a “triangle number” (where that number of things can be stacked to make a triangle shape, like a human pyramid). Each pair of towers adds to 13, and there are 6 pairs (1+12, 2+11, etc. up to 6+7) so we get 13 x 6 = 78. That’s why for a triangle with n things along the bottom row, the total will be n x (n+1)/2.

And thank you Catherine M. for sending this hilarious video!

Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.