You have a list of 100 numbers with values in the sequence 1 to 100. Each number of the sequence appears once except that one value is missing and one value is repeated. Determine which value is missing and which one is repeated.
Notice that I didn't say anything about writing code. If asked,I will answer no questions like "are they in order?" and so forth.
It puts most people at ease, but for people with certain character flaws it is like dropping them in the ocean 20 miles from the coast with no life jacket.