नकारात्मक अंकन (निगेटिव मार्किंग): अनुमान लगाना कब सही रहता है?

Most state PSC Prelims papers take marks off for a wrong answer. UPPSC, MPPSC and CGPSC deduct one-third of the question's marks, UKPSC one-fourth, HPSC 0.25 marks. (Check your exam's page on this site for the current rule.)

The rule of thumb

Say a right answer gets 1 mark and a wrong one loses p marks. If you can narrow a question down to k options and pick one at random:

Expected marks = 1k × 1 − k − 1k × p

A guess is worth taking when this is above zero, which means

p < 1k − 1

With one-third negative marking (p = 13)

Options left	Expected marks	Guess?
4 (no idea)	14 − 34 × 13 = 0	No gain
3	13 − 23 × 13 = 19	Small gain
2	12 − 12 × 13 = 13	Yes

What this means in the hall

• A blind guess among four options gains nothing on average and adds risk. Leave it.
• Once you can rule out two options, answering is clearly worth it.
• With one-fourth marking the blind guess is still worth about 116 of a mark, so the line moves slightly in favour of attempting.
• Some papers have their own rules. RPSC gives a fifth option for "not attempting" and penalises leaving questions blank, and HPSC can disqualify you for leaving more than 10% unanswered. Learn your paper's rule before exam day.