Subjects
Mathematics
--Algebra
--Applied Math
--Arithmetic
Social Studies
--Holidays
Grade
3-5
6-8
9-12
Brief Description
Present this fun calendar math challenge to students at any time of year.
Objectives
Students will
Keywords
calendar, math magic, puzzle, math, mathematical thinking, language of math
Materials Needed
Lesson Plan
Present this fun calendar math challenge to students at any time of year. The start of a new year is a great time for this activity because most students will have access to some old (preferably unused) calendars for the year just ended; or perhaps you have a good source of calendars for the year now starting.
Display on a board, chart or screen a calendar page such as the one below.
Here are a few sample calendar pages:
Sample calendar page
More calendar pages
Select any section of the calendar that includes a 3-by-3 square grid (3 rows of three numbered squares) as highlighted in the above image.
Circle the three numbers that appear in the center row of the calendar section you have selected (11, 12 and 13 in the sample above).
Then circle the three numbers that appear on the right diagonal that begins at “4” (4, 12, and 20) and the left diagonal that begins at “6” (6, 12, and 18).
Challenge students to add the numbers that comprise the three circled calendar rows.
Wow -- the center row and two diagonals each add up to the same number!
11 + 12 + 13 = 36
4 + 12 + 20 = 36
6 + 12 + 18 = 36
Provide each student with a page (one month) from a calendar. Challenge them to select 3 or 4 sections of the calendar and see if the “calendar magic” that happened on your sample calendar section holds true on their own calendar pages. Can any student find an example of a calendar section where this “magic” does not work?
Provide students with a sheet of paper and challenge them to put into words (see “Math Communications” standards below) the “magic math” behind the calendar sections on their pages. What do they see that surprises them? Can they express how this magic works?
Bonus Challenge!
Introduce students to Education World’s It All Adds Up! math puzzle series.
Assessment
Assess students’ mathematical thinking/communications skills based on their written expressions of the math behind the calendar “trick.”
Lesson Plan Source
EducationWorld.com
Submitted By
Gary Hopkins
Math Subject Center
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Lesson Planning/Math Archive
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It All Adds Up Puzzles (Printable Work Sheets)
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