Spy Game Lesson
Spy Game Lesson Plan
Abstract
Students will learn how to do modular math and use it to decipher encrypted messages.
Standards (NCTM 3-5)
Algebra
Understand patterns, relations, and functions
- represent, analyze, and generalize a variety of patterns with tables, graphs,
words, and, when possible, symbolic rules;
Represent and analyze mathematical situations and structures using algebraic symbols
- recognize and generate equivalent forms for simple algebraic expressions and
solve linear equations
Student Prerequisites
- Technological:
Students must be able to:
- perform basic mouse manipulations such as point,
click and drag.
- use a browser such as Netscape for experimenting with
the activities.
Teacher Preparation
Teacher will need:
- Encrypted codes for the students to decipher.
Students will need:
- Access to a browser
- paper
- pencil
- scissors
Lesson Outline
- Focus and Review
- Have a clock drawn on the board with hands aligned as if it were 12:00.
- Ask the students according to the clock on the board what time it would
be in:
- 3 hours
- 8 hours
- 13 hours
- 28 hours
- 334 hours
- Ask students to think about the answers for a moment. See if they can
recognize a pattern that might make it easier to calculate an answer for
the "What time will it be in 334 hours question?"
- Objectives
Students will demonstrate their ability to use modular math by deciphering several
encrypted codes.
- Guided Practice
- Explain to the students that an easy way to calculate what time it will be in
x number of hours is to divide x by the number of hours on the face of the
clock (the mod), take the remainder, and count that far on the clock.
- Introduce this method in writing. For example: 334 mod 12.
- Have students calculate:
- 36 mod 6
- 53 mod 8
- 420 mod 22
- Tell the students to check their answers by using the
Clock Applet.
- Have the students convert the alphabet into numbers setting A=0, B=1, C=2, etc.
- Tell the students to write a short sentence about themselves that they won't mind
someone else reading.
- Have the students convert the letters in their sentence to numbers using the
alphabet numbers they just calculated.
- Explain the term shift.
- Have the students shift their numbers by 5
and convert their list back into letters.
- Explain that their sentences should now look like a bunch of letters.
- Have the students swap messages and try to decode them using their
current knowledge.
- Teacher Input
- Explain to the students how to decipher an encrypted message if they are given
the shift.
- Explain the term multiplier.
- Explain how to decode a message if they are given the multiplier.
- Independent Practice
- Have the students pair up and open the Caesar's Cipher applet.
- Have each student use the computer to encrypt a message by changing
the constant value.
- Tell the students to swap messages with someone else in the class.
- Instruct the students to decode the message they received from their classmate.
- Now, have the students encrypt a message using a multiplier.
- Have the students swap messages and decode the message they receive
- Explain that the messages you are about to pass out have been
intercepted from a company that has discovered the fountain of youth
and that the encrypted messages will lead them to the fountain.
- Hand out several messages for the students to decipher.
- Have the pairs of students work to decipher the codes.
- In order to ensure that each partner is doing an equivalent amount of work
require that each student must be responsible for deciphering at least 3
messages.
- Closure
- Once the first group has finished give the class 10 more minutes to work on
completing deciphering their messages.
- Instruct the groups to take turns playing with the Caesar's Cipher 2
applet recording the original message, the encrypted message, and the correct
shift and multiplier.
- Decipher each of the fountain of youth messages with the class to review how
to properly decode messages with a shift and or a multiplier.
Please use this form for questions and comments about this project.
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