In view of what I said in my comment regarding the previous question, I have to concede that this is a bit more interesting than the opening of the Forth Road Bridge. But I still think that to ask for the exact year is a bit mean.
Much better, IMHO, not to give the decade but to give some leeway (say, two years either way).
On the other hand ... the question mentions that Mandela was in prison for 28 years, and that is surely a big clue. I would suggest that people are much more likely to remember the year in which he was released, rather than the year he was imprisoned.
So why not ask for that year?
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