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

Problem : 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 Ananya

Solution :

Let No. of questions attempted correct by Jyanti  = x
No. of questions attempted incorrect by Jyanti = 120 - x

ATQ

x(1) - (120 - x)(1/2) = 90
x - 60 + x/2 = 90
x + x/2 = 90+60
(2x+x)/2 = 150
3x/2 = 150
3x = 150 × 2
3x = 300
x = 300/3
x = 100

∴ No. of questions she attempted correctly is 100