contains Seven multiple choice type of questions carrying One
mark each
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Candidate get 3 marks fot every right question and −1 mark for every incorrect answer.
If the candidate attempts all of 10 questions, then from the set 15,16,17,18,19,20,.he can only achieve the score of 18, by marking 7 coorect options and 3 incorrect option.
If he attempts any more or less than 7 questions, then the score becomes out of the range of the set. Only if he does 7 correct questions, he can score 18 out of given set.
Now we know to get a score of 18, the candidate needs to correct only 7 questions out of 10, it means he will mark 3 questions incorrectly.
So number of possible combinations to get a score of 18 consists the number of ways he can chose the 7 correct answer multiplied by number of way he can incorrect the 3 questions.
Hence number of possible distinct combinations will be 10
C
7
.(3)
3
Where (3)
3
are the number of possible way he can incorrectly mark the 3 questions, as every question has 3 incorrect choice out of 4. So for 3 questions, it will 3.3.3=(3)
3
If the candidate attempts all of 10 questions, then from the set 15,16,17,18,19,20,.he can only achieve the score of 18, by marking 7 coorect options and 3 incorrect option.
If he attempts any more or less than 7 questions, then the score becomes out of the range of the set. Only if he does 7 correct questions, he can score 18 out of given set.
Now we know to get a score of 18, the candidate needs to correct only 7 questions out of 10, it means he will mark 3 questions incorrectly.
So number of possible combinations to get a score of 18 consists the number of ways he can chose the 7 correct answer multiplied by number of way he can incorrect the 3 questions.
Hence number of possible distinct combinations will be 10
C
7
.(3)
3
Where (3)
3
are the number of possible way he can incorrectly mark the 3 questions, as every question has 3 incorrect choice out of 4. So for 3 questions, it will 3.3.3=(3)
3
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