# This Week From Bedtime Math: Your Body, By the Gallon

Why do people love splashing around in water? Maybe because it&s splashing around in us! Come do some liquid number crunching in today&s math challenge.
By Laura Overdeck
Feb 04, 2014

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Feb 04, 2014

What is Bedtime Math? A message from Laura: Bedtime Math is a pretty simple idea: We all know we should read to our kids at night, but what about math? My husband and I have done fun, mischief-loaded math problems with our kids at night for years, and when at age 2 our third child started hollering for his own math problem, we realized we were onto something:  In a world where so many people say, "Ewww, math!" we had created a household culture where kids don't just tolerate math, they actually seek it out. Now, every week, we'll be posting a new problem right here on Scholastic Parents!

As you know, the inside of your body doesn't look anything like the outside — it isn't just skin all the way through. You have a heart, stomach, brain, and other organs, and you have little tubes called arteries and veins that carry blood through you, and bones that hold you up. What's crazy is how much each of these parts weighs. More than half your weight is just water -- yes, plain old water like what comes out of the faucet. And when you were born, it was closer to 3/4 of your total weight! We just don't notice, since all that water is mixed into your blood and other materials like your skin. Speaking of which, your skin is your biggest organ: a grown-up's skin by itself weighs about 20 pounds! Meanwhile, bones take up about 1/7th of your weight. But water still wins, so the next time you're thirsty and drink some water, think of it as putting more of you back in you.

Now that we've piqued your interest, see if your kids can come up with the answers to these water-inspired word problems.

Wee ones: If your friend down the street weighs 31 pounds and then drinks 1 pound of water (2 cups), now how much does he tip the scales?

Little kids: If you're carrying 5 pounds of bone and 6 pounds of skin, how much would you weigh if you were just "skin and bones"?  Bonus: If a grown-up's skin weighs 20 pounds and the rest of her weighs 100 pounds, how much does she weigh in total?

Big kids: If you weighed 8 pounds when you were born and 3/4 of that was water weight, how many pounds of water did you have?  Bonus: If by age 4 you weighed 40 pounds and exactly half of you was water, how much water weight did you gain by then?

Wee ones: 32 pounds…when you weigh yourself, the scale counts everything in you!

Little kids: 11 pounds.  Bonus: 120 pounds total.

Big kids: 6 pounds, since a quarter of your weight was 2 pounds.  Bonus: 14 pounds, since by then you contained 20 pounds of water.

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