In this question, we are concerned with knowing the number of questions on a quiz, given that Deana had a certain percentage after scoring an amount of marks.
We proceed as follows;
Let the number of questions on the quiz be X.
Now, she got 85% by making 3 incorrect choices. This means the percentage of questions she got incorrectly would be 100-85 = 15%
what we are saying is that it is just 15% of her questions that were wrong.