When the family car developed a slight knock, the husband asked his wife if she had bought regular or premium gas, but she couldn't remember.

"You probably got the cheaper gas," he said. "That could account for the engine running so rough."

"No, the gas wasn't cheaper!" she replied indignantly.

"Well, how much did it cost?" asked the husband.

"It cost the same as always," said the wife. "I bought the usual thirty dollar's worth."