Question

A person comes into a store and say to the shopkeeper, "I will buy half of your eggs plus half of an egg. "The transaction is made. A second person comes into the store and makes the same transaction. So does a third. The shopkeeper notices tha he now has one egg left. How many eggs did he begin with?

Answer 1

Work backwards:
After every time a customer buys half of the eggs there are N eggs left.
So before the transaction, there were
2*(N + 1/2)=what was there before.
Repeat the same three times you'll get what was there at the very beginning.

Answer 2

12

Answer 3

12 and a half