Anna gives three pupils at We Solve Problems (Jacob, Leonhard and Sophie) the following puzzle. She writes down three different numbers on pieces of card, and asks each of the three pupils to hold up their cards. She asks them to do this in such a way that they can’t see their own card, but that the other two people can see theirs.
Sophie sees that Jacob has \(8\) and
Leonhard has \(12\). Anna then tells
them that two of the cards add up to the third.
Sophie says ‘I don’t know my number.’
Leonhard says ‘I also don’t know my number.
What is Sophie’s number?