Clone of Secret Codes
Why do this problem?
This problem practises working systematically on addition and subtraction. The activity requires some lateral thinking.
Possible approach
You could start by showing the group how the letters are turned into numbers and that A is both $1$ and $27$.
This sheet might be useful.
The first piece of code, given in numbers, could be done as a whole group. Next it would be a good idea to change some letters into numbers. The children could, for example, change their own names. These could then be put into code by adding 3 to each letter number and changing back into letters.
Take, for example, "William".
WILLIAM in numbers is - $23. 9. 12. 12. 9. 1. 13.$
Adding $3$ to each letter - $26. 12. 15. 15. 12. 4. 17.$
Turned back into letters - Z L O O L D Q
Perhaps they could work out each others' names and then change them back into the correct letters.
After this the group could work in pairs on the problem as given. Then at the end of the lesson could get together again to show what they have done.
Key questions
What letter does $32$ [for example] stand for?
What letter does your name start with? What is the number for it?
What are you going to add/subtract ?
How do you think you can turn that back so you can read it?
How do you reverse adding $3$/subtracting $2$?
Possible extension
The last part of the problem is reallly an extension. When this has been done learners could make up their own pieces of code.
Possible support
Some children who have problems with reading or slight dyslexia may find this work extremely difficult. You could suggest just turning letters into numbers and back again as in the very first part of the problem or doing a quite different piece of work.