Here is an encoded message, a message that has been converted into a code.

WRGDB LV D JRRG GDB.

Can you figure out what it says in English? How was the original message encoded?

1. Now it’s your turn to write a secret code!

   1. Write a short and friendly message with 3–4 words.

   2. Pick a number from 1 to 10. Then, encode your message by shifting each letter that many steps forward or backward in the alphabet, wrapping around from Z to A as needed.

      Complete these tables to create a key for your cipher.

      position in the alphabet	1	2	3	4	5	6	7	8	9	10	11	12	13
      letter in the message	A	B	C	D	E	F	G	H	I	J	K	L	M
      letter in code

      position in the alphabet	14	15	16	17	18	19	20	21	22	23	24	25	26
      letter in the message	N	O	P	Q	R	S	T	U	V	W	X	Y	Z
      letter in code

   3. Give your encoded message to a partner to decode. If requested, give the number you used.
   4. Decode the message from your partner. Ask for their number, if needed.

2. Each letter can be represented by a number. For example, F is 6 because it is the 6th letter of the alphabet. 

   • Complete the first 2 rows of the table to convert between letters and numbers.
   • Complete the third row by adding or subtracting the number you chose in the last problem to find the coded letter number.
   • Complete the fourth row by converting the coded number to a letter.

   letter in message	F	I	S
   message letter number	6			8
   coded letter number
   letter in code
3. Use and to write an equation that can be used to encode an original message into your secret code.
4. Use and  to write an equation that can be used to decode your secret code into the original message.