how many answers have been answered correctly?

Question

In the math competition it is determined that the correct answer will get a score = 2, the wrong answer will get a score = -1, while if you don't answer will get a score = 0. Of the 75 questions given, 10 questions are not answered. The score obtained by this student was 103. How many answers have been answered correctly?

Answer 1

2C + (-1)W = 103

C+W = 75-10 = 65

C =65-W

2(65-W) -W = 103

130-2W-W = 103

3W = 130-103 = 27

W = 27/3 = 9 incorrect answers

C = 65-9 = 56 correct answers

56(2) -9 = 112-9 = 103