Suppose she answered question X correctly and question Y incorrectly.

{ x+y & lt； =20 ①

4x-y=60 ②

}

(2) where x=(60+y)/4 is an integer, and y

So y=0 or 4 or 8 or 12 or 16, in which 8, 12 and 16 are omitted.

So there are two kinds. 1. Correct answer 15, wrong answer 0, no answer 5 questions.

2. Correct answer 16, wrong answer 4 questions, no answer 0;