Question

Aneek gave a math exam of 21 questions.Each question done right gives him 20 marks.Each question done wrong gives him -10 marks.If Aneek attempted all the questions and if he got 300 marks,then how many questions are done wrong by Aneek?(please answer the question with a proper process.)

Answer 1

Let the right answers be x and wrong be (21-x)
According to the question
20x+(21-x)*-10=300
20x-210+10x=300
30x=300+210
x=510/30
x=17
21-x=21-17=4