If Gunnar gives you a cookie will have twice as many he give the same number of cookies How do does have?

Let's say Gunnar gives you x cookies. Then he would have 2x cookies left. Because he gave you the same number of cookies that he kept for himself, we know that x = 2x. Dividing both sides of the equation by x, we get 1 = 2. This is impossible, so there must be an error in our reasoning.

The error is in the assumption that Gunnar has cookies and that he can divide them.