Wendy obtained 75 marks in a physics test which consisted 20 questions. 6 marks are awarded for each correct answer, 3 marks are deducted for each wrong answer. If she answered all the questions, how many questions did she answer correctly? Use try, check, revise method to solve.
Let's assume that Wendy answered "x" questions correctly.
The number of questions she got wrong would be "20 - x" since she answered all the questions.
The number of marks she received for the correct answers would be 6x since 6 marks are awarded for each correct answer.
The number of marks deducted for the wrong answers would be 3(20 - x) since 3 marks are deducted for each wrong answer.
Total marks received = Marks obtained for correct answers - Marks deducted for wrong answers
75 = 6x - 3(20 - x)
Expanding and simplifying the equation:
75 = 6x - 60 + 3x
Combining like terms:
75 = 9x - 60
Adding 60 to both sides of the equation:
135 = 9x
Dividing both sides of the equation by 9:
x = 15
Therefore, Wendy answered 15 questions correctly.