Most of the competitive exams being held now days offers multiple choice questions (abbreviated MCQs), so even a person who don't have any idea about the solution may answer a guess from available option, unlike in case of conventional exam where one go for a solution only if he has to write something fact-full with respect to question asked.
If number of possible options associated with question is 4(option A, B, C, D ), and one makes a guess for answer he get the right answer in one of the each four trials. Since there are four options for each question and correct answer for a question is distributed over four options A, B,C and D. There would be equal chances for all of the options to be correct(i.e. 1/4 or 25% each). If one choose to mark 4 consecutive questions with option C, he will be correct with at least (as average) one guess out of four.
This is known as probability in mathematical studies, probability stands for chances. If one has to randomly choose one of the available option out of the four option provided the chance of being it correct would be 1/4 or 0.25 or 25%.
With only two option given for a question and making guess for one out of two question will result in probability of making 1/2 or 0.50 or 50 % of it correct.
In another case if five options are given with reference to a question and one has to guess an answer he can guess on out of five, that means 1/5. Since number of options are 5 in this case at least 1 out his 5 guesses would be correct and we can say that chances or probability of getting a right answer is 1/5 or 0.20 or 20% in this case. As we see number of options increases chances (probability) of guessing a correct answer is decreasing.
Its good from the perspective of aspirant giving a 4 option MCQs exam, he may have a chance to get 25% easily without knowing anything useful and by just making random guesses.
But the teacher, administrative or anyone conducting exam does not want any one to score based on random guesesses, the purpose of exam is to screen only reward marks based of knowledge of the individual. So how to deal with guessers, here Negative marking comes into picture but how much?
Let, Fill is math teacher he conducts a MCQ based test for his students with 4 options provided with every question on the test sheet, also each question carries equal makes and that is equal to 1. He knows that if one goes with guessing 1 out of 4 questions will be correct, but at the same time 3 will be incorrect. He wants to reward something for incorrect options so that this guessing pattern of 3 incorrect and 1 correct(luckily) out of 4 question will result in zero marks. He assumes to assign 'N' marks for incorrect answer
so
Number of incorrect guess * N + marks of correct guess * marks for correct answer = 0
3*N + 1* number for correct answer = 0
By making this way overall effect of guess results in zero, if N= -1/3 of marks for correct answer.
(if 1 mark is decided for every correct answer, -1/3 will be for incorrect answer)
If number of options provided for each question is 2. Due to random guess 1 out each 2 answers will be correct(luckily) and 1 will be incorrect(mathematically). in this case
1*marks for incorrect answer guess(N) + 1* Marks for correct answer = 0
which provides, marks for incorrect guess equal to minus of marks for correct answer.
In case of questions with five options negative marking is equal to minus of one fourth of marks for correct answer by following similar calculation.
QuickFact Writer has got 36 % (>25% yeahh!) of maximum marks by guessing all the answer with option B in a 4 option based MCQ exam with zero negative marking. This could be happen because correct answer is randomly distributed over A, B, C and D. We give equal weight (25% each in this case) to every possible choice in study of Probability.
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