In a competitive examination, 1 mark is awarded for . . .

Question : In a competitive examination, 1 mark is awarded for each correct answer while 1/2 mark is deducted for every wrong answer. Jayanti answered 120 questions and got 90 marks. How many questions did she answer correctly? 

Doubt by Pari

Solution : 

Let the number of questions answered correctly = x

and the number of questions answered incorrectly = y

ATQ 

x(1) + y(-1/2) = 90

Multiply both sides by 2

2x-y=180 — (1)

Also 

x+y=120 — (2) 

Solving equation (1) and (2) by elimination method

2x-y=180

 x+y=120
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3x+0 = 300
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x=300/3

x=100

Putting in equation (2)

100+y=120

y=120-100

y=20

Number of Questions answered correctly = 100

Number of Questions answered incorrectly = 20