To get exactly 90% you need to miss 5.6 questions.
You can miss 10% of questions, or 12 questions
22 questions
.8 x 30 = 24 so you can miss 6 questions
40
24 of them.
35
6 of them.
Providing that all the other questions are correct then it is 9 questions
25 questions missed
20
No more than 15.But why miss any ?
Just one question, and I reckon it was the question about percentages!