Ok, DD is 7yo in her second year of school in Switzerland. (They don't start until 6yo)
She has this homework, translated from French
Use each time the numbers 3 5 and 8.
Form 2 3-digit numbers in such a way that the difference between these 2 numbers is either:
a. the greatest possible
b. the smallest possible
Is that not a bit advanced? They are only doing very basic maths at the moment, adding and subtraction.