Calendar Math
By Michael Naylor

Online Extra: Calendar Math Activities

While some of these activities work well with a large classroom calendar, for others you may wish to supply each child with a copy of the month's calendar page .

Yesterday, tomorrow and next week (Grades K-2)
Use relationships between days to develop number relationships. Point at today's date and ask, "What day will it be tomorrow? What day was it yesterday? What day will it be in one week?" Then ask, "What day was it one week before January 12? What day will be it be one week after January 22?" With older children, you can hide the calendars and ask the same kind of questions. After you elicit answers, show them the calendar page to check.

Mystery day (Grades K-4)
Give clues so your students can find a mystery day. "My day is on a Thursday. It has a 3 in it." Or, "My day is on a weekend. It's an even number and is greater than 20." Then ask students to write a set of clues to determine a special day and try them out with their classmates.

Days left (Grades 2-4)
Point to a day on the calendar and ask, "How many days until the end of the month?" See how many different ways your class can find to figure out the answer and list the ways on the board. One way is to count each day, another is to count by sevens, moving up a week at a time until the last week, then count up from that number to the last day. Yet another way is to subtract the chosen start day from the number of the last day. Once you've accumulated several strategies, ask students to use a particular method so they get practice with each.

Practice multiples of seven by extending the ending day to some time next month or the month after. For example, ask your students to count by sevens to find out how many days from January 5 to February 23 (they'll count by sevens up to 49).

Find a sum or difference (Grades 2-4)
Choose a number, say 25, and ask your students to find pairs or trios of numbers that make 25. Or, choose a number and ask them to find two numbers that differ by that amount.

For an interesting pattern hunt, have your students find pairs of numbers that differ by 7 or 14. What do they notice about these numbers? (They both fall on the same day of the week!)

Calendar boxes (Grades 3-6)
Outline a 2 x 2 box on the calendar such as shown here:

Have your students add diagonally opposite numbers. What do they notice about the pairs? (The sums are the same.) Now have them add the numbers vertically. How do the sums compare? (They differ by 2.) What about adding them horizontally? (They differ by 14.)

Have your class outline a different 2 x 2 box and try finding diagonal, vertical and horizontal sums again. Do the same relationships hold? Ask your students to figure out why these rules apply.

Fast box addition (Grades 6-8)
Have a student choose a 2 x 2 box and demonstrate how you are able to quickly give the total. Tell your students the secret: Add 4 to the first number and multiply the result by 4. Have the class test the result on several boxes.

The secret is algebra; if the first number is x, the other numbers are x + 1, x + 7 and x + 8. The total is 4x + 16, which is the same as 4(x + 4).

Have your students outline a 3 x 3 box and ask them which is greater – the sum of all of the numbers or 9 times the center number? Relabel the center number as x and write all the other numbers in terms of x as shown here:

When adding all of those terms, the constants cancel (–8 + 8 = 0, –7 + 7 = 0, etc.) so all that is left 9x. The total of all nine numbers, then, is 9 times the center number.

Have fun!

Online Extra: Calendar Math Activities

Michael Naylor is a professor of math education at Western Washington University, Bellingham, WA.

January, 2007, Vol.37, No.4