This big box adds something to any number that goes into it. If you know the numbers that come out, what addition might be going on in the box?
Shapes are added to other shapes. Can you see what is happening? What is the rule?
Here's a very elementary code that requires young children to read a table, and look for similarities and differences.
A case is found with a combination lock. There is one clue about the number needed to open the case. Can you find the number and open the case?
Letters have different values in Scrabble - how are they decided upon? And would the values be the same for other languages?
Can you follow the rule to decode the messages?