New Puzzler: String Puzzler, Number A

RAY: You have in your possession two pieces of string. Let's say that each is a couple of feet long, but it doesn't really matter. And they can both be different lengths, it doesn't matter either. And they're burnable, like the fuses that they use to, you know, light dynamite. Now you could light either end of either string, and it would burn. In fact, if you lit one end of a string, it would burn in exactly an hour. Are you with me so far?

TOM: I've got it.

RAY: So, you light a string with what? The Zippo lighter. And it's lying on the table or on the floor.

TOM: -- It would burn right along and it would take one hour to be gone.

RAY: But here's the wrinkle: the strings do not burn at a constant rate. For example, the string might burn for two minutes and then go crazy and burn like mad and then slow down, and da-da-da. You don't know what rate the string's burning at any specific time. All you know is that in an hour's time, the whole string is burned. It's not linear. And not predictable.

TOM: Gotcha.

RAY: So, the question very simply is, with the Zippo lighter and these two strings, how would you measure 15 minutes of time?

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[ Car Talk Puzzler ]