Investigation Organizer: Grade 5, Chapter 3

## Crack the Code

Summary: Cryptographers are people who put messages in code. They use combinations of letters, numbers, and mathematical ideas. Your group will create a code, and then try to crack a coded message from another group.

1. Plan It

A. Start your code. List the letters of the alphabet. Leave five lines blank after each letter.

B. Write a number. Below each letter, write a number.

• A will be 1.
• B will be 2.
• C will be 3, and so on.

Our list completed

2. Put It Together

Keep coding!

Take your time while completing each of the following steps.

1. Factor each number. For prime numbers, show the number 1. For example, C = 3, so write 1 x 3.

2. Remove the multiplication sign to get the code number. For C, the code number will be 13.

3. To make your code different from the codes of other groups, multiply each code number by a number between 11 and 25. For example, if you picked 11, C would become 13 x 11, or 143.

Coding completed

3. Wrap It Up

A. Use your code. Use your group's number code to write a sentence. You can use a sentence in a book, or make one up. Separate each number that represents a letter with a slash.

B. Use your decoding power. Exchange your coded sentence with another group. See which group can decode the other group's sentence first.

HINT: You will not have a remainder when you divide the letter number by the secret code number.

Decoding completed

• Did you use your math skills to create and decipher codes?
• Is your factoring list clear and correct?
• Is your coded sentence accurate?
• Did your group organize and divide the work fairly?
• What other mathematical ideas could be used to create a code?

Review completed