Each window of the safe is one place of the secret number. The letters above tell which: O is ones, T tens, H hundreds, Th thousands, TTh ten-thousands and HTh hundred-thousands.
Every clue tells something about one place or about the whole number. Start with a clue that names a digit directly and write it in.
Finally check all clues against your number. Exactly one number fits.
Example
For parents
What does this exercise practice?
The child reads big numbers place by place and sees that every digit gets its value from its place. Working out one number from several partial clues practices place value, digit sums and logical elimination all at once.
Common pitfalls
Places often get mixed up: the ten-thousands digit is not the number 10,000 but only the digit in the fifth place from the right. The digit sum also gets confused with the number itself.
How to practice at home
Pick a number from the newspaper or a car odometer and give each other clues until the other person guesses it.
Related: Test cards, Number riddles