In a class test (+3) marks are given for every correct answer and (-2) marks are given for every incorrect answer and no marks for not attempting any question.
(i) Radhika scored 20 marks. If she has got 12 correct answers, how many questions has she attempted incorrectly?
(ii) Mohini scores – 5 marks in this test, though she has got 7 correct answers. How many questions has she attempted incorrectly?
(iii) Rakesh scores 18 marks by attempting 16 questions. How many questions has he attempted corrrectly and how many has he attempted incorrectly?
(i) It is given in the question that,
Marks given for every correct answer = +3
And,
Marks given for every wrong answer = - 2
Also, it is given that:
Marks obtained by Radhika = 20
Correct answer = 12
Therefore,
Marks obtained for correct answers = 12 × 3
= 36
Hence,
Marks obtained for incorrect answers = Total marks – Marks obtained for correct answers
= 20 – 36
= - 16
As, marks obtained for 1 wrong answer = - 2
Hence,
Number of incorrect answers = 
= 8
(ii) It is given in the question that,
Marks given for every correct answer = +3
And,
Marks given for every wrong answer = - 2
Also, it is given that:
Marks obtained by Mohini = - 5
Correct answer = 7
Therefore,
Marks obtained for correct answers = 7 × 3
= 21
Hence,
Marks obtained for incorrect answers = Total marks – Marks obtained for correct answers
= -5 – 21
= - 26
As, marks obtained for 1 wrong answer = - 2
Hence,
Number of incorrect answers = 
= 13
(iii) It is given in the question that,
Marks given for every correct answer = +3
And,
Marks given for every wrong answer = - 2
Total marks obtained by Rakesh = 18
Number of questions attempted by him = 16
Therefore,
3 × Correct answers + (-2) × Incorrect answers = 18
3 × Correct answers + (-2) × (16 - Correct answers) = 18
5 × Correct answers + (-32) = 18
5 × Correct answers = 18 + 32
5 × Correct answers = 50
Correct answers = 
= 10
Hence,
Incorrect answers = 16 – 10
= 6