Answer:
Student A and Student B both answered 2 questions correctly.
See explanation below
Explanation:
Note: that answers in the form:

ARE ALL EQUIVALENT.
First of all, 4/5 is equivalent to 0.8 if we do long division.
and 19/20 is 0.95 if we do long division.
Now, Student A:
Both of the fractions are correct and the negative sign is equivalent and makes the answer correct, so both are correct.
For Student B:
Similarly, both answers are correct for this student as well, looking at the equivalence we showed first.
Also, "-" (negative) in front of the parenthesis and inside parenthesis here doesn't matter.
Hence,
Student A and Student B both answered 2 questions correctly.