### Still Unsolved

20 mathematical questions were given to a student. For each correct question, the student was promised 10 chocolates. However, for every wrong question, it was decided that he would have to give back 5 chocolates.

To get maximum number of chocolates, the student answered all the 20 questions. As a result, he got some answers wrong and got 125 chocolates at the end of evaluation.

Can you calculate how many answers he gave were incorrect ?

### 4 guesses to Calculate How Many Answers

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• Frank

15 right and 5 wrong

150 – 25 = 125.

Algebra:
R=right
W=wrong
R+w=20 or w= 20-R
10R – 5W = 125
Sub for W
10R – 100 + 5R = 125
15R = 225
R = 15

• brent

Oh yeah, I also got “5 incorrect answers” as the solution.

My thinking was: 200 chocolates for getting them all correct.
Each wrong would reduce that by 15 (10 missed points for not getting it right, and 5 pay-back penalty).
Since the student was 75 points sort of perfect 200 – 125).
75 / 15 = 5 incorrect answers.

• Crabman

Frank, brent your different approaches makes me curious about your MBTI classification. Do you know? if not arealme dot com had a decent test they call “Vocational Personality Radar Test”.

If this is all greek to you, if you’re ever bored look up MBTI test yourself however you like, and read the personality profile. Interesting way to get some self-awareness.

FWIW I’m ENTP

• Frank, you win again!
5 questions.
Explanation: This question can be solved using a simple trick. If all the questions were answered correctly, the student would have 200 chocolates. For every wrong answer, he will lose 5 chocolates and he will also lose 10 chocolates that he would have gained if he would have answered correctly. Thus, for every wrong answer, you have to deduct 15 chocolates from 200. 200 – 125 = 75. 15 * 5 = 75 . Hence, he gave wrong answer for 5 questions.