3 marks are awarded for each answer and 1 mark deducted for each wrong answer.a boy attempted 30 questions and scored 50 %. How many questions did he get wrong ?

Answer 1

It is not clear to me what 50 percent. The max score is 90, fifty precent is 45, which wont work out. I think your teacher did not mean to put the percent mark, but rather meant a score of 50.

(30-W)3-W=50
4W=40
wrong W=10 Correct=20

Answer 2

max, mark is 90,50 % is 45,he got 50 %,he got 45,if 3=1 que,45=15que,he got 15 que,there are 30ques,so 30-15=15,ans=15Q