Question 25
Châu writes a four-digit number and asks Dũng to guess it. Dũng asks, “Is it 2896?” Châu replies, “Exactly one digit is correct, and it is in the correct position.” Dũng asks, “Is it 5273?” Châu replies, “Exactly two digits are correct, but both are in the wrong positions.” Dũng asks, “Is it 1702?” Châu replies, “All four digits are correct, but all are in the wrong positions.” What number did Châu write?
