# Lesson: Calendar Math

Subjects

Mathematics

--Algebra
--Applied Math
--Arithmetic

Social Studies
--Holidays

3-5
6-8
9-12

Brief Description

Present this fun calendar math challenge to students at any time of year.

Objectives

Students will

• add numbers that appear on the center-row horizontal and the diagonals in a section of nine (3 x 3) calendar squares.
• think about and express their reflections about the math behind this bit of “calendar magic.”

Keywords

calendar, math magic, puzzle, math, mathematical thinking, language of math

Materials Needed

• calendar pages (one month per page), preferably unmarked; one calendar page to a student
• paper and pencil

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:

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

National Standards

LANGUAGE ARTS: English

NL-ENG.K-12.3
Evaluation Strategies
NL-ENG.K-12.4 Communication Skills
NL-ENG.K-12.5
Communication Strategies
NL-ENG.K-12.6
Applying Knowledge
NL-ENG.K-12.7 Evaluating Data
NL-ENG.K-12.12
Applying Language Skills

MATHEMATICS: Number and Operations

NM-NUM.3-5.1
Understand Numbers, Ways of Representing Numbers, Relationships Among Numbers, and Number Systems
NM-NUM.3-5.3
Compute Fluently and Make Reasonable Estimates
NM-NUM.6-8.1 Understand Numbers, Ways of Representing Numbers, Relationships Among Numbers, and Number Systems
NM-NUM.6-8.3 Compute Fluently and Make Reasonable Estimates
NM-NUM.9-12.1
Understand Numbers, Ways of Representing Numbers, Relationships Among Numbers, and Number Systems
NM-NUM.9-12.3
Compute Fluently and Make Reasonable Estimates

MATHEMATICS: Algebra
NM-ALG.PK-2.1
Understand Patterns, Relations, and Functions
NM-ALG.3-5.1
Understand Patterns, Relations, and Functions
NM-ALG.6-8.1
Understand Patterns, Relations, and Functions
NM-ALG.9-12.1 Understand Patterns, Relations, and Functions

MATHEMATICS: Communications
NM-COMM.PK-12.1
Organize and Consolidate Their Mathematical Thinking Through Communication
NM-COMM.PK-12.2 Communicate Their Mathematical Thinking Coherently and Clearly to Peers, Teachers, and Others
NM-COMM.PK-12.3
Analyze and Evaluate the Mathematical Thinking and Strategies of Others NM-COMM.PK-12.4 Use the Language of Mathematics to Express Mathematical Ideas Precisely

Education World
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