Answer: Suppose 80 percent of spouses are F's — "faithfuls" who try their best to keep a marriage going. The other 20 percent are N's — "nasties," impossible to get along with over the long haul. You can estimate your own percentages, but everybody knows the types.

Now out of every 200 people marrying for the first time — 100 couples — 64 of the marriages, on average, will involve two F's (.8 times .8 equals .64) and will endure.

An average of 32 of the 100 marriages will involve an F and an N — and eventually break up. Four of the 100 marriages will be between two N's — ill-fated from the start.

It's apparent the overall divorce rate for this first round is 36 marriages out of the 100, or 36 percent.

OK, round 2: All of the F's who married F's are still together and not in the re-marriage pool. From the 32 divorced F-and-N couples, there will now be 32 F's and 32 N's making the dating rounds. From the 4 divorced N-and-N couples, there will be 8 N's. Total: 32 F's, 40 N's!

These 72 former spouses will form 36 new marriages. But only about seven of these, on average, will be F-and-F. The remaining 29 will be N-and-F, or N-and-N, and soon end. Divorce rate for round 2? A whopping 80 percent. Overall divorce rate for both rounds will be close to 50 percent.

For round 3, you can see the faithful F's are scarcer still, the nasty N's are in abundance, and marriage licenses might as well be printed in disappearing ink.

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Send STRANGE questions to brothers Bill and Rich at strangetrue@compuserve.com, coauthors of "Can a Guy Get Pregnant? Scientific Answers to Everyday (and Not-So- Everyday) Questions," from Pi Press.