Question 1 - Case Based Questions (MCQ) - Chapter 3 Class 10 Pair of Linear Equations in Two Variables (Term 1)

Last updated at Aug. 17, 2021 by Teachoo

A test consists of ‘True’ or ‘False’ questions. One mark is awarded for every correct answer while ¼ mark is deducted for every wrong answer. A student knew answers to some of the questions. Rest of the questions he attempted by guessing. He answered 120 questions and got 90 marks.

Type of Question

Marks given for correct
answer

Marks given for correct answer

True/False

1

0.25

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Question A test consists of ‘True’ or ‘False’ questions. One mark is awarded for every correct answer while ¼ mark is deducted for every wrong answer. A student knew answers to some of the questions. Rest of the questions he attempted by guessing. He answered 120 questions and got 90 marks.Question 1 If answer to all questions he attempted by guessing were wrong, then how many questions did he answer correctly?Let Number of questions whose answer he knew = x
Number of questions attempted by cheating = y
Given that
Total Questions attempted = 120
x + y = 120
Also, answer to all questions he attempted by guessing were wrong
Marks from all guessed answers = y × (−𝟏)/𝟒
Marks from all attempted answers = x × 1
Now,
Total marks = 90
x − 𝑦/4 = 90
4x − y = 90 × 4
4x − y = 360
Thus, we need to solve
x + y = 120 …(1)
4x − y = 360 …(2)
From (1)
x + y = 120
y = 120 − x
Putting value in (2)
4x − y = 360
4x − (120 − x) = 360
5x − 120 = 360
5x = 360 + 120
5x = 480
x = 480/5
x = 96
Putting value of x in (1)
y = 120 − x
y = 120 − 96
y = 24
Number of questions he answered correctly = x = 96
Thus, he answered 96 questions correctly
Question 2 How many questions did he guess?
Number of questions he guessed = y = 24
∴ He attempted 24 questions by guessing
Question 3 If answer to all questions he attempted by guessing were wrong and answered 80 correctly, then how many marks he got?
Given that
Total questions = 120
Questions answered correctly = 80
Thus,
Questions answered by guessing = 120 − 80 = 40
Now,
Total Marks = Question answered correctly × 1
− 1/4 × Questions answered incorrectly
= 80 × 1 − 1/4 × 40
= 70
Thus, he got 70 marks
Question 4 If answer to all questions he attempted by guessing were wrong, then how many questions answered correctly to score 95 marks?
Given that
Total questions = 120
Let Questions answered correctly = x
∴ Questions answered by guessing = 120 − x
Now,
Total Marks = Question answered correctly × 1
− 1/4 × Questions answered incorrectly
95 = x × 1 − 1/4 × (120 − x)
95 = x − 1/4 × (120 − x)
95 × 4 = 4x − (120 − x)
380 = 4x − 120 + x
380 + 120 = 5x
500 = 5x
5x = 500
x = 500/5
x = 100
Thus, he answered 100 questions correctly

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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