Below are three aptitude questions that would require you to apply your logical thinking to arrive at equations, following which you need to solve those to arrive at correct answer. Hope these questions help you.
Ashok got thrice as many sums wrong as he got right. If he attempted 60 sums in all, how many sums did he solved correctly?
a) 20 b) 12 c) 15 d) 10
Answer : c) 15
Let the number of answers got correct by Ashok be X and the number of wrong answers be 3X.
Since he attempted 60 sums, X + 3X = 60
4X = 60
X = 15
So, Ashok had solved 15 sums correctly.
In an examination, there are 100 questions, 4 marks for each correct answer and 2 marks for each wrong answer. If Surya attempted all the 100 questions and scored 40 marks. Find the number of questions he answered wrongly?
a) 30 b) 40 c) 70 d) 60
Answer : d) 60
Let the number of questions Surya answered correctly be X and the number of questions that Surya answered wrongly be 100 – X. (so that the total number of answered questions is 100)
Marks scored by him is 40.
Given that 4 marks for each correct answer and 2 marks for each wrong answer , i.e 4X - 2 (100 - X) = 40
6X = 240
X = 40
Hence, Surya answered 60 questions wrongly.
In an Entrance examination, a multiple choice question has 5 options. If Rohit chooses the correct option, he earns 4 marks and for choosing the wrong option incurs negative marks. If Rohit chooses an option randomly, his expected score is 0. Suppose Rohit has successfully eliminated 3 incorrect options. What will be the expected score if he chooses randomly among the remaining options ?
a) 1 b) 2/3 c) 3/2 d) 0
Answer : c) 3/2
Given that Rohit can get 4 marks for each correct answer.
Let the marks for a wrong answer be X.
Probability of getting correct answer = 1/5 and Probability of getting wrong answer = 4/5.
Given that on selecting randomly, Rohit's expected score is 0. Putting this in the form of a formula :
His Expected Score = 0 = (Probability of getting correct answer ) x (score for correct answer) + (Probability of getting wrong answer ) x (score for wrong answer)
i.e. (1/5) x 4 + (4/5) x X = 0
X = -1 = Score for wrong answer.
If Rohit had eliminated 3 wrong options, then the Probability of getting correct answer is 1/2 and probability of getting wrong answer is 1/2.
Then his expected score is 1/2 x (-1) + 1/2 x 4 = 3/2.