SarwaSamadhan

Negative marking: when should you guess?

नेगेटिव मार्किंग: अनुमान कब लगाएं?

A blind guess is worth almost nothing, but ruling out even one option makes guessing pay off under ¼ and ⅓ negative marking. Here is the arithmetic and a simple rule to follow in the exam hall.

बिल्कुल अंधा अनुमान लगभग बेकार है, लेकिन एक विकल्प भी हटा सकें तो ¼ और ⅓ नेगेटिव मार्किंग में अनुमान फायदेमंद है।

The expected value of a guess

Expected marks = (chance of being right × 1) − (chance of being wrong × penalty). With four options and a blind guess, the chance of being right is 1/4.

Example ¼ negative marking (SSC, Railway, IBPS), blind guess
1/4 − 3/4 × 1/4 = 1/16 ≈ +0.06 marks per question — almost nothing
Example ⅓ negative marking (UPSC prelims style), blind guess
1/4 − 3/4 × 1/3 = 0 — no gain on average
Example One option ruled out, ¼ penalty
1/3 − 2/3 × 1/4 = 1/6 ≈ +0.17 marks per question
Example One option ruled out, ⅓ penalty
1/3 − 2/3 × 1/3 = 1/9 ≈ +0.11
Example Two options ruled out, ⅓ penalty
1/2 − 1/2 × 1/3 = 1/3 ≈ +0.33

A rule for the exam hall

  1. Sure of the answer → mark it.
  2. Can rule out at least one option with a real reason → guessing pays on average; mark your best choice.
  3. No idea at all → skip it, especially with ⅓ negative marking.
  4. Do not change answers on a vague feeling; change only when you find a definite mistake.

Use time, not luck

Guessing helps at the margin. Marks really come from attempting every easy question first: do one round of the paper picking quick wins, then come back for the slower ones.

Try it yourself · अभ्यास

  1. With ¼ negative marking and 4 options, how much is a blind guess worth on average?
    Show answer

    +1/16 of a mark (about 0.06)

  2. You can eliminate two options and the penalty is ⅓. Should you guess?
    Show answer

    Yes: 1/2 − 1/2 × 1/3 = +1/3 mark on average