A fellow was walking along a country road when he came upon a farmer working in his field. The man stopped and called out to the farmer "How long will it take me to get to the next town?"

The farmer didn't answer. The guy waited a bit and then started walking again. After the man had gone about a hundred yards, the farmer yelled out "About 20 minutes.”

“Thank you. But why didn't you tell me that when I asked you?"

“Didn't know how fast you could walk".