Negative Marking: When to Guess and When to Skip

Example 1: four options, penalty one-quarter mark

A pure guess has a 1 in 4 chance (0.25).

• Gain: 0.25 × 1 = 0.25
• Loss: 0.75 × 0.25 = 0.1875
• Expected value: +0.0625

A blind guess is very slightly positive on average.

Example 2: four options, penalty one-third mark

• Gain: 0.25 × 1 = 0.25
• Loss: 0.75 × 1/3 = 0.25
• Expected value: 0

A blind guess is break-even. Since it also adds risk, there's no real advantage.

Example 3: eliminate one option

With four options, if you can rule out one, your chance rises to 1 in 3.

• Penalty 1/4: 1/3 − (2/3 × 0.25) ≈ +0.17
• Penalty 1/3: 1/3 − (2/3 × 1/3) ≈ +0.11

Both are positive, so an informed guess is worthwhile.

The rule of thumb

Situation	Suggested action
Can eliminate at least one option	guess
Pure guess, small penalty (about 1/4)	acceptable but not important
Pure guess, larger penalty	skip
No negative marking	attempt every question

Important cautions

1. Check the rules. Penalties differ between exams and can change, so read the latest official notice.
2. Some sections may have no penalty.
3. Your accuracy matters. A guess isn't the same as a skilled estimate.

Practical strategy

1. Answer what you know first.
2. Mark uncertain questions and return to them.
3. Use elimination on the rest.
4. Guess only when you've narrowed it down.
5. Don't change answers without a good reason.

Don't let this rule your exam

Negative marking is one factor. Accuracy in what you know matters more, and calm decisions matter most.

Practice

Practising MCQs teaches you to feel when you truly know an answer, and when you're guessing.

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