This must be awfully embarrassing:
The question carried four marks — a score capable by itself of taking students to within a mark of the math subject cut-off of five. Only on clearing subject cut-offs are students eligible to be considered for IIT seats.
The results this year also revealed that math scores of around 6,700 general category students selected were separated by just 87 marks — translating into an average of 77 students on every mark between the topper and the last entrant.
For those selected, four marks, on an average, would mean a rank jump of over 300, enough to secure them a more popular stream of engineering than the one offered.
The picture becomes even worse when you take into account the negative mark for a wrong answer.
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In GATE (an exam that I am familiar with), the answers are circulated to all the participating institutions -- the IITs and IISc -- as soon as the exam is over. A set of people in each institution pores over question paper to see if everything hangs together. Whenever a potential problem is located (such as two possibly correct choices when the student is asked to choose only one, or the absence of the correct answer in the four choices, ambiguous wording, etc), an appropriate action -- including removal of the problematic question from consideration -- is taken.
Even this procedure has its flaws. By the time a mistake is discovered, some damage has already been done: some students would have wasted their time answering a question that's removed from evaluation, or they would have been thrown off -- or, emotionally upset -- by a poorly worded question.
But, the mistake in math JEE comes well after the results are out; it is really surprising that it slipped through the JEE's stringent controls -- probably more stringent than those for GATE -- at multiple levels.
I wouldn't be surprised if the IITs end up facing a bunch of lawsuits.