# Today From Bedtime Math: Backwards Water Slide

What happens when a waterslide goes backwards? Find out in this fast-flowing challenge from Bedtime Math!
By Laura Overdeck
May 19, 2015

Ages

3-13

May 19, 2015

Have you ever slid down a water slide? It's just a slide with water running down it to make you zoom really fast. But we bet you haven't ridden a slide where the water runs up. Check out the Flow Rider, a giant slide where swimmers can ride bellyboards and surfboards on a nonstop wave coming at them. Flow Rider pumps water at super-high speed straight up the hill, while you fling yourself and your board on top of the water. These kids are riding on their bellies, but some brave folks stand on long skinny boards to surf. The water is so strong that some kids were flung up to the top of the slide and right over the edge! How much water does it take to make a wave like this – and how long can you ride it without wiping out?

Now see if you and your kids can come up with the answers to these math questions:

Wee ones: On which side of that photo is someone already sliding, the left or the right?

Little kids: Only 1 kid at a time can ride on each side. If there were 3 people riding on each side, how many riders would that be?  Bonus: If 2 of those were surfing instead of bellyboarding, how many would be bellyboarding?

Big kids: Everyone wanted to ride the Flow Rider, so there was a long wait. If 8 people are in line in front of you and only one slide is open, and a new person gets to start every 5 minutes, how long do you have to wait for your turn?  Bonus: What if both sides are open and people who get the left side ride for 10 minutes, but people who land on the right get to ride for just 5 minutes? Now how long until your turn?

The sky's the limit: We're told that it costs more than \$500,000 for a park to build a Flow Rider. If it cost exactly \$500,000, how does that relate to a million dollars? And how many of these could a hotel chain build for \$10 million?

Wee ones: On the right.

Little kids: 6 riders.  Bonus: 4 bellyboarders.

Big kids: 40 minutes.  Bonus: Just 25 minutes. After 10 minutes 3 people will be done, then another 3 after another 10 minutes, then the next two people start but one will ride for only 5 minutes, and you can take that person's place.

The sky's the limit: 20 Flow Riders. \$500,000 is half a million, so for \$1 million they can build 2 Flow Riders. That means \$10 million can build 20 of them.

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