Examination 2

In an examination, a teacher awards 2 marks for every correct answer and subtract a mark for every wrong answer. If there are 20 questions and a child scored 25 marks how many correct answer did the child get?

Correct answer:

c =  15

Step-by-step explanation:

25 = 2c - 1•(20-c)

25 = 2•c - 1•(20-c)

3c = 45

c = 15

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