A man wanted to get into a members only club so he hide and watched the guard at the door of the club house. The guard said a number to each member as they approached, and the member would respond with a number of their own. If the member responded with the correct number they were let in. If they responded incorrectly they were thrown out.
One member came up to the door, the guard said twelve, and the member responded with six and was let in. Another member came to the door, the guard said six and the member responded with three and was let in.
Believing he had heard enough, the reject went up to the guard. The guard said ten, and the reject said five, but was not let in. What should the reject have said?