A Backwards Day

A Backwards Day

September 19, 2019

A palindrome is a word that is spelled the same backwards and forwards, like toot and racecar. Can you think of any others? It turns out numberscan do the same thing — like today’s date! Today is written as 9/19/19, which means the 19th day of the 9th month (September). In fact, we’re just ending a whole stretch of palindrome days, starting with 9/10/19 up to today. Don’t forget, 9/1/19 was a palindrome, too! We’ve been having cool streaks like this for the past few years, like 8/13/18, and 7/12/17…see if can you figure out when they happen, and when they don’t!

Wee ones: How do you say “123” in backwards order?

Little kids: If you say “221” in backwards order, is it the same or different? How about 454?   Bonus: How old will you be the next time your age is the same backwards and forwards?

Big kids: If you add up all the digits in today’s date (9 + 1 + 9 + 1 + 9), how much greater is the sum than the sum of the digits of this month’s first palindrome, 9/1/19?  Bonus: The digits of 9/1/19 add up to 20. What’s the next date that will add up to 20 this way?

The sky’s the limit: If you’re allowed to write both the month and year as 2 digits, when’s the first year when we won’t have any palindromic dates? (For example, in 2020 you can write February as 02).













Wee ones: 321.

Little kids: 221 then reads 122, so it’s not a palindrome. But 454 does work!  Bonus: Different for everyone…any single digit works, like 7, 8 or 9! Or your next age might be 11, or 22…or 101!

Big kids: It’s 9 more. You can actually figure this out without doing any addition – there is one more 9 in today’s date, and all the other digits are the same! Bonus: 10/9/19 is the next date with digits that add up to 20. You know it can’t be a September date, because 9/x/19 gives you a sum of 19. October dates give you a sum of 11 between the month and year (10/x/19 = 1 + 0 + 1 + 9 = 11). If 11 + x = 20, then x must equal 9.

The sky’s the limit: We’ll have the same kinds of dates in 2019 (/10/19, 9/11/19…), and in 2020 we can have them in February (02/1/20 through 02/9/20, plus 02/11/20). We’ll also have a couple in 2021 (for example: 1/2/21, 1/21/21, and 12/1/21 through 12/9/21, as well as 12/11/21 and 12/22/21). Then in 2022 we’ll have 2/2/22, 2/20/22, 2/21/22 and so on. That’s true throughout the ’20s, with dates like 3/20/23, all the way through 9/29/29. In 2030 we start over with 03/1/30, then 1/3/31. This pattern will continue through the ’40s, ’50s, all the way to 9/9/99 in 2099. 2100 is the first year we won’t have one, because we can’t have 0/0/00!

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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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