To pass the certification, you will need a minimum 70 percent pass mark.

Here, you have answered 90 questions correctly. 1 mark for each. So it would be 90 marks. Let us say the remaining 30 were wrong. .5 will be deducted for each. So, 30*.5 = 15

Now your total will be 90-15=75 marks.

Calculate your percentage, (75/120)*100 = 62.5

You could leave the remaining 30 unanswered. So, it would increase your chance of getting the pass mark.