Question

in a test +5 are given for every correct answer and -2 marks for every incorrect answer.rita answered all the questions and scored 30 marks through she got 10 correct answers how many incorrevt answers had she attempted

Answer 1

5 marks for correct
-2 marks for incorrect
so rita scored 30
10 correct which means 10×5=50
so 50 - x =30
x= 30 - 50
x= 20
so she answered 20/2=10 incorrect answers

Answer 2

For correct answer = +5. For wrong answer = +(-2).
The no. of correct answers are 10. So, 5*10 = 50 marks are rewarded to Rita. But the total score is 30.
So, you have to do 50 - x = 30 where 'x' is the score awarded for incorrect answer. So, x = 20 (50-30 = 20). 
She attempted 10 wrong questions because 20/-2 = -10 where we should neglect "-" sign because they asked for no. of questions. Let's verify it. Then you will get clarification:

(5*10) + (-2*10)
= 50 + (-20)
= 50 - 20
= 30 is her score. So it is verified