Truth-Teller & Code Reasoning

How the lesson starts: Truth-Teller & Code Reasoning

Parrot Island
Ahoy! Welcome to Parrot Island. Some parrots are truth-tellers. They only ever say true things. A treasure chest is locked with a secret code. Let's check the facts and crack the code!
Could a truth-teller say it?
A truth-teller can only say something that's really true. 12 is even. True, so yes! 9 is a multiple of 3. True, so yes! 7 is greater than 15. False! A truth-teller could never say that.
Two-clue code
The first lock has two clues. Clue 1: the first digit is 4. Clue 2: the last digit is 2. Which code fits: 472, 572 or 473? 572 breaks clue 1. 473 breaks clue 2. Only 472 fits both!