An algebra problem by Mateus da Silva

Algebra Level 2

On a certain 25-question test, each correct answer is worth 4 points, and every wrong answer is worth -1 point. Daniel answered all questions and scored 65 points. How many questions did Daniel got right?


The answer is 18.

Mateus da Silva by Mateus da Silva , 22, Brazil

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2 solutions

Blank Rough
Sep 27, 2015

Let x be the number of correct answers and y be the number of wrong answers

[1] x + y = 25 equation 1 is the number of answers or questions

[2] 4x - y = 65 equation 2 is the total score

Now you have a system of linear equations. Add equation 1 and 2

5x = 90

x=18

2 Helpful 0 Interesting 0 Brilliant 0 Confused

total points = 4 x right answers -1 x (25 = right answers)

65 = 4c - (25 - c)

65 = 4c - 25 + c

90 = 5c

c = 18

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