A woman with a baby walked into a doctor's office. She asked if they could weigh the baby. A nurse said that the baby scale was not working that day, but what they could do is weigh the mother while she was holding the baby, and then weigh the mother by herself, and subtract.

The woman thought about this for a minute. "It wouldn't work," she said, after a while, "I'm not the mother; I'm the grandmother."