Can You Drink a Whole Lake?

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.

Can You Drink a Whole Lake?

November 12, 2015

We got another awesome question from a Bedtime Math fan: Carmel P. wants to know, could you drink a whole lake in an hour? Well, for starters, you’d better hope it’s a small lake. Look at a 1/2 gallon of milk: that’s already a lot to drink. Now imagine a cube 1 foot wide in each direction… that cube holds 8 gallons, or 16 of those cartons. Now imagine a square swimming pool: if it’s 20 feet wide, 20 feet long and 10 feet deep, it holds 20 x 20 x 10 or 4,000 cubic feet of water — or 64,000 of those milk cartons! NOW imagine a square-ish lake that’s almost 1/2 mile wide — let’s say 2,000 feet each way — and 100 feet deep. That holds 10 of those swimming pools across, 10 pools from back to front, and 10 layers of pools top to bottom…you’d have to drink 1,000 swimming pools in an hour, or about 1 every 3 seconds.

As it turns out, a person can continuously drink only 1/4 gallon each hour or you get sick (from thinning out your blood). So how many people could drink that lake in an hour? Let’s find out!

Wee ones: If you could drink 5 whole swimming pools, what numbers do you say to count them?

Little kids: If you drink 10 swimming pools of water and a “little” lake holds 14 pools of water, how many pools’ worth of water do you have left to drink?  Bonus: If you make it to only halfway between 10 and 14, how many swimming pools do you drink in total?

Big kids: If a lake holds “just” 8 million gallons, how many people can drink it down in 1 hour with each person drinking just 1/4 gallon? (Hint if needed: That means it takes 4 people to drink each gallon.)  Bonus: If you could drink 10 whole swimming pools every 10 minutes, could you empty a 100-pool lake in 1 hour?

The sky’s the limit: Lake Superior in the U.S. holds 3 quadrillion gallons of water! Can you “spell” 3 quadrillion in digits? Hint: A quadrillion is one thousand trillions, and a trillion is one thousand billions.




Wee ones: 1, 2, 3, 4, 5.

Little kids: 4 more swimming pools.  Bonus: 12 pools.

Big kids: 32 million people, because each gallon needs 4 people tackling it. That’s almost all the people in Canada.  Bonus: No: there are only 6 10-minute chunks in an hour, so you could drink only 60 pools in an hour. Another way to think of it: 10 pools in 10 minutes is 1 pool per minute, so that’s 60 in an hour.

The sky’s the limit: 3,000,000,000,000,000 gallons!

And thank you Carmel for this swimmingly great math question!

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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 while still in diapers, 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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