Playing with Calendar Patterns

11 Years Ago This Month…

My book business had been on hiatus for nearly 15 years, as I focused on homeschooling five children. I posted on forums and blogged off and on, but the old books fell into (not entirely undeserved) oblivion.

Now my older kids were moving out into their adult lives, and I’d begun to think about publishing again. I dusted off the old manuscripts to see what could be salvaged and began my adventure of indie publishing.

And all the gurus agreed, every author needed an email newsletter.

Share a playful math activity every month? Sure I could do that!

So while I revised and edited the manuscript for Let’s Play Math, to be published in paperback that fall, I launched my first “Playful Math” email, with an idea that’s still fun all these years later: Play math on your calendar.

For Elementary Children

Any internet search can turn up a variety of printable calendars. Choose your favorite.

Young children can use the calendar as a number line to do addition and subtraction beyond what they might normally handle. Look for addition and subtraction patterns:

• 3 + 5 = ? Now go to 13 + 5, and 23 + 5.
• What do you notice?
• What do 11 − 7, 21 − 7, and 31 − 7 have in common?
• Take turns finding and describing patterns.

Older children can practice their times tables:

• Mark the numbers you hit when you count by 2.
• What pattern do they make?
• Make the counting-by-3 pattern, or mark the 7s, etc.
• Which counting-by patterns are your favorites?
• What happens if you start at a weird number, like counting by 6s but starting at 5?

What other patterns can you discover?

Algebra “Magic” Patterns

Try some of Cynthia Lanius’s algebra calendar puzzles…

The Basic Square: Ask a friend to secretly choose four calendar dates that all touch each other and form a square. (For example, 18, 19, 25, and 26.) The friend should add those four numbers together and tell you the sum.

Then you “magically” identify the dates!

(Your secret: Divide the sum by 4, then subtract 4. The answer is the first date of your friend’s square.)

The Advanced Square: For a tougher puzzle, ask your friend to make a square with nine dates, three rows of three. (For example, 11–13, 18–20, and 25–27.) Again, secretly add the numbers and say only the sum.

Again, you can “magically” find their chosen dates.

(This time, divide the sum by 9. That answer is the center date of your friend’s square.)

• Using what you know about calendar patterns, can you explain WHY the calendar magic works?

Don’t peek! But the answers are here:

• Fun with Calendars
  (the Basic Square)
• More Fun with Calendars
  (the Advanced Square)