On marking correctly one question a boy gets 5 marks and 2 marks are deducted on marking a wrong response. He attempted 85 questions but got 285 marks. How many did he mark correctly?
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Answer:
marks of correct answer = 325
Step-by-step explanation:
let the correct answer = x
and incorrect answer = y
A.T.Q
x + y = 85 ----------(1)
5x - 2y = 285 --------(2)
multiply by 2 in eq 1
2(x + y = 85)
2x + 2y = 170 ------------(3)
on adding eq 2 and 3
5x - 2y = 285
2x + 2y = 170
7x = 455
x = 455/7
x = 65
put x in eq 1
x + y = 85
65 + y = 85
y = 85 - 65
y = 20
correct answer = x = 65
incorrect answer = y = 20
marks for correct answer = 5x = 5 × 65
= 325
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