"Do not guess" is the advice everyone gives, and it is wrong often enough to cost marks. The honest answer depends on how much you can eliminate, and the arithmetic is worth doing once so you never have to do it in the hall.
The expected value of a blind guess
Four options, no information. You are right one time in four and wrong three times in four:
(0.25 × +4) + (0.75 × −1) = 1 − 0.75 = +0.25 marks
Positive — but thin. Over forty blind guesses that is ten marks, and the variance is enormous. It is not a strategy so much as a coin you are allowed to flip.
What elimination does to the number
| Options eliminated | Chance of being right | Expected marks |
|---|---|---|
| None | 1 in 4 | +0.25 |
| One | 1 in 3 | +0.67 |
| Two | 1 in 2 | +1.50 |
| Three | certain | +4.00 |
Eliminating a single option nearly triples the expected value. Eliminating two makes attempting clearly correct — a 50/50 guess is worth one and a half marks, and refusing it costs you that.
The three situations you are actually in
- You know it. Answer and move on. The risk here is not the marking scheme; it is re-reading the question until you talk yourself out of a correct answer.
- You can narrow it. Attempt. Two options left is worth +1.5 marks on average, and over a paper those add up faster than the occasional minus one subtracts.
- You have nothing. This is the only case where blank is defensible — and even then it is a near-break-even decision, so it comes down to whether the minute is better spent elsewhere.
The mistake the arithmetic hides
All of this assumes your elimination is sound. A candidate who believes they have narrowed it to two, but has actually ruled out the correct answer, is not making a +1.5 bet. They are making a guaranteed −1.
That is why this is a revision problem rather than a strategy problem. Confident elimination comes from knowing the material; no amount of expected-value reasoning substitutes for it.
What to practise
In a full-length mock, mark each question you attempt as knew it, narrowed it, or guessed. Then compare against the answer key. If your "narrowed it" attempts are scoring worse than one in three, the problem is not your nerve — it is that your elimination is wrong, and that is fixable.