How to Make a River Green

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.

How to Make a River Green

March 17, 2018

It’s St. Patrick’s Day, the feast when we dye our least favorite foods green to see if they’ll taste better that way. Today people will dye just about anything green, including their hair, their pets…and in Chicago, the river running through town. So how do they do that? Amazingly, the dye is an orange powder — it turns green only when it hits the water! At 9:15 in the morning of the parade, 2 boats go out into the water: a bigger boat holding 4 plumbers, and a smaller boat with just 2 plumbers. The guys on the big boat sprinkle the orange powder over the water using flour sifters. Then the smaller boat follows to make waves and spread the color. The 25 pounds of dye keep the river green for about 5 hours — plenty of time to show off your green hair.

Wee ones: If the big boat has 4 people on it and the little boat has 2 people, what numbers would you say to count all those people?

Little kids: Back when Chicago used 100 pounds of dye, the river stayed green for 5 days! If March 17 was the 1st day, what date was the 5th day?  Bonus: If that first day was a Tuesday, what was the 4th day of green river?

Big kids: If the dye goes in at 9:15 in the morning and lasts 5 hours, until what time will the river stay green?  Bonus: About 400,000 people go to the Chicago parade. How many more would need to show up to make it a million?

The sky’s the limit: One favorite green object for St. Patty’s is the very rare 4-leaf clover: if you pick 10,000 clovers, you’ll find only 1 that has 4 leaves. If all the rest have 3 leaves, how many 3-leafers will you have?




Wee ones: 1, 2, 3, 4, 5, 6.

Little kids: March 21st.  Bonus: Friday.

Big kids: 2:15 in the afternoon.  Bonus: 600,000 more people.

The sky’s the limit: 9,999 clovers.

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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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