This post would be suitable for all MCQ based exams with negative marking. But, I will explain things by keeping UPSC CSP in mind.
In CSP there is a negative marking of 33% i.e. for every wrong answer you loose 1/3rd of a questions marks. Breaking it down further, if you make guess in 4 questions and 1 among them is correct and 3 are wrong then you get zero marks.
Negative marking is introduced so that people don’t just get through the exams by making guesses.
But, in light of cut throat competition and ever increasing cut offs it becomes necessary to make some calculated guess.
This post will help you understand the risk involved in your guess in following scenarios:
- You have removed two options i.e. you now need to make guess among only 2 remaining options
- You have removed one option i.e. you now need to make guess among three remaining options.
- You have no idea whatsoever and you are making a blind guess by choosing any of the 4 options.
To start with, let us understand some basics:
33% negative marking means you need 1 right answer for every 3 wrong guesses if you don’t want to loose marks i.e. if go for guessing and attempt 4 questions by guessing, you just need one question to be correct to be safe. If you manage to correctly attempt more than one question, than you gain some marks.
Now, lets break it down further:
CASE 1: Two options removed
In such questions, you are able to remove 2 options and you don’t know anything about other 2. You only choice is to make a guess and choose one from the two options.
Let us assume that you have attempted 4 such questions. Now let us calculate what are the chances that you won’t loose marks.
There are 1/2 chances that your answer may be wrong/right because there are 2 options only.
To loose marks, all 4 attempted questions must be wrong i.e. so probability of occurring it is (1/2)*(1/2)*(1/2)*(1/2) = 1/16 i.e. in 15 out of 16 cases you will gain marks. And if god as decided to ruin your fate, than there are 1 in 16 chances of you loosing marks.
So, my advice would be attempt all such questions. Don’t leave them.
CASE 2: One option is removed
In such questions, you are able to remove 1 option and you don’t know anything about other 3. You only choice is to make a guess and choose one from the three options.
Let us assume that you have attempted 4 such questions. Now let us calculate what are the chances that you won’t loose marks.
There are 2/3 chances that your answer may be wrong because there are 3 options and 2 of them are wrong.
To loose marks, all 4 attempted questions must be wrong i.e. so probability of occurring it is (2/3)*(2/3)*(2/3)*(2/3) = 16/81 i.e. in 65 out of 81 cases you will gain marks.
So, my advice would be attempt such questions when you are not sure you will get through i.e.
- When you are able to attempt only <60 questions with all your knowledge/ticks and CASE 1.
CASE 3:Totally blind guess
In such questions, you don’t know anything. You have to do “akkad bakkad” and decide 😛
Let us assume that you have attempted 4 such questions. Now let us calculate what are the chances that you won’t loose marks.
There are 3/4 chances that your answer may be wrong because there are 4 options and 3 of them are wrong.
To loose marks, all 4 attempted questions must be wrong i.e. so probability of occurring it is (3/4)*(3/4)*(3/4)*(3/4) = 81/216 i.e. in 135 out of 216 cases you will gain marks. It is very high risk
So, my advice would be that you should not attempt such questions.
Sorry for including bit of maths, but there was no option.
These calculation are based on assumptions of Probability.
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