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.

Answer 1

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.