Answer: Zahid obtained 170 marks.
Step-by-step explanation:
Let's start with the basic rules of the question.
We know that for each question answered correctly, 5 marks will be given. And for each incorrect answer, 3 marks will be deducted. Now the problem says that Zahid's marks have been deducted by 18. There are 3 marks deducted for each wrong answer so we'll divide 18 by 3, which gives us 6. Zahid got 6 questions wrong. However, there are 40 questions in the exam, so if we assume that the only ones he answered incorrectly are the 6 questions, then we should subtract 6 from 40. This leaves us with only the correct answers left which is 34. Now again, we know that for each correct answer 5 marks will be given. Assuming that Zahid answered the rest of the questions correctly, we should multiply 34 by 5, which gives us 170.
In numbers your workings might look like this:
18 ÷ 3 = 6
40 - 6 = 34
34 × 5 = 170
I hope this helped you answer your problem. Please let me know if you need any further explanation :)