Okay, from previous hints, cheating is part of it, marriage is part of it, and divorce would likely be the "failure" part of it. Piece it all together, then read the original question and you should be able to nail it.
I can't vouch for the validity of the figure "75%", but I see no error there. It's easy to understand that the divorce rate is high among couples who at least one of them started off by cheating on someone else.
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