You are going to visit your grandmother on Mother's day. You want to give her two cakes. However, to get to her house you must cross seven bridges. At each bridge is a troll who demands ½ of all of your cakes as the price to pass. However, this troll, being a nice troll, feels bad and gives you back 1 of the cakes that he took.
The puzzle to solve: How many cakes must you leave with to be able to give your grandmother 2 cakes