I couldn't hear her friend's response, but my guess is that she looked dubious. The woman went on to explain her secret.
"I don't fill up.
Whenever I go the pump, I buy $20 worth of gas. That's how much I spent at the pump before the price increases, and that's how much I'm spending now.
I was able to stick around only long enough to hear her comment on the lack of common sense these days. Due to her friend’s soft-spoken nature, or shyness developed from the realization that a stranger was eavesdropping, I’ll never know what was said in response.
Part of me feels guilty that I didn’t interrupt the conversation with a back of the napkin algebraic formula. After all, it’s not difficult to demonstrate that at a fixed total cost, the number of gallons purchased goes down when the price per gallon goes up. But then again, how do you go about doing such a thing without coming across like a total jerk?