A Problem by Swapnil Das

Algebra Level 2

There are 48 questions in a test. Each correct answer fetches 1 mark, for each wrong answer 1/2 mark is deducted. A student got 21 marks and he attempted all the questions.Find the no. of questions answered wrongly.


The answer is 18.

Swapnil Das by Swapnil Das , 20, India

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2 solutions

Caleb Townsend
Feb 28, 2015

Let x x be the number of questions answered correctly, and y y be the number of questions answered incorrectly. Since y = 48 − x , y = 48 - x, we can solve for the number of correct answers based on the score. x − 1 2 ( 48 − x ) = 21 x - \frac{1}{2}(48 - x) = 21 3 2 x = 45 \frac{3}{2}x = 45 x = 30 x = 30 Now the number of incorrect answers is y = 48 − 30 = 18 y = 48 - 30 = \boxed{18} Perhaps the student will do better after spending some time on Brilliant!

4 Helpful 0 Interesting 0 Brilliant 0 Confused

That's right!

Swapnil Das - 6 years, 3 months ago

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I didn't understand this sum clearly ...could anyone pls help me ?? How did 3/2x come after the above equation ???

Karuna Shree - 5 years, 1 month ago
Noel Lo
May 26, 2015

x x is the number of questions answered wrongly so ( 48 − x ) (48-x) were answered correctly.

( 48 − x ) − x 2 = 21 (48-x) - \frac{x}{2} = 21

3 x 2 = 27 \frac{3x}{2} = 27

3 x = 54 3x = 54

x = 18 x= \boxed{18}

2 Helpful 0 Interesting 0 Brilliant 0 Confused

Nice! Excellent!

Swapnil Das - 6 years ago

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