Sleeping and Swimming – at the Same Time!

Here's your nightly math! Just 5 quick minutes of number fun for kids and parents at home. Read a cool fun fact, followed by math riddles at different levels so everyone can jump in. Your kids will love you for it.

Sleeping and Swimming – at the Same Time!

July 6, 2017

If only we humans could sleep as well as animals. They somehow manage to catch z’s even when they’re on the move. For water animals who need to breathe air, they have no choice: they can’t just sink to the ocean floor while napping! So dolphins let 1/2 of the brain sleep while the other half is awake, with one eye open. While the left half sleeps, the right eye is shut, then vice versa. Seals also sleep this way, leaving one flipper ready to flap around. Air-breathing water animals need to solve other kinds of problems – like otters, who tie their tails around seaweed to keep from floating away while they nap. And albatrosses can actually sleep while flying! You really have to wonder what kinds of dreams these animals have.

Wee ones: Close your 2 eyes. Now open both. Now see if you can wink: try to close just 1 eye!

Little kids: If 3 seals and 3 dolphins are napping, each with 1 eye open, how many eyes are closed?  Bonus: If there are 10 dolphins and 1/2 of them are sleeping with 1 eye open and the rest are wide awake, how many open eyes do they have altogether?

Big kids: Sloths, the laziest animals out there, sleep as much as 20 hours in one day. If you sleep just 10 hours a night, how much more than you does a sloth sleep in a week?  Bonus: If an albatross flies for 2 hours and sleeps 1/5 of the time, how many minutes of sleep does it get? (Reminder: An hour has 60 minutes.)

The sky’s the limit: Suppose a bunch of dolphins are trying to nap, and those who are succeeding each have 1 eye open. If there are the same number of awake dolphins as sleeping dolphins, and there are 40 more open eyes than closed ones, how many dolphins are there in total, and how many are asleep vs. awake?




Wee ones: Do your best to give a wink!

Little kids: 6 eyes closed.  Bonus: 15 eyes: 10 open eyes on the 5 awake dolphins, and 5 open eyes on the sleeping ones.

Big kids: 70 more hours, since it sleeps 10 hours more than you each day.  Bonus: 24 minutes (1/5 of 120).

The sky’s the limit: There are 40 dolphins, 20 of whom are awake and 20 of whom are sleeping. Every awake dolphin has 2 open eyes, and for each of those dolphins there’s another dolphin with 1 open eye and 1 closed.  So each asleep/awake pair has 3 open eyes and 1 closed — which means there are 3 times as many open eyes as closed for the whole group. Since the open number is 3 times the closed number, the gap between them is the same as 2 sets of closed eyes (2/3 of the total opens). 40 is 2/3 of 60, so there are 60 open eyes and 20 closed. That must mean 20 1-eye-sleeping dolphins.

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About the Author

Laura Overdeck

Laura Overdeck

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.

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