Puzzle | premium:Tip-Top Magic Numbers Mind Reading Card

This premium from the manufacturer of an enriched white bread offered their customers a sure way to impress their friends. The cards came with these instructions: "Hand out the seven Tip-Top Magic Number Cards. Ask someone to take his age or any number and return all cares to you on which the chosen number appears. You can determine this number by adding the first number in the upper left corner, on the cards which are returned to you." Your friends would surely be astounded by your genius when you had devined the correct number; if you wanted to credit the comsumption of enriched Tip-Top bread for your intelligence, the baking company would not mind at all.