Question 2.
2.1:    Most got this wrong. Many gave an example where the proof fails,
but did not identify the flaw in the "inductive proof".
2.2:    Most students could not finish the inductive step, some mixed up
variable names 'n' and 'k' in the inductive step.

Question 3.
3.1:    most got this right, solved it numerically. Some got the
algorithm for GCD right, but didn't know what number was the GCD.
3.2:    most either got it entirely or did not write anything relevant.

Question 4.
Most students did well.

Question 5.
5.1:    Few students got the second part: (n+m)/2 lies between n
and m and therefore is composite. Most got the first part.
5.2:    Didn't know how to check only for prime divisors <=
sqrt(number). Didn't show result of division. You were asked to show
all work.

Question 6.
6.1:    Some students used properties of congruences (not allowed by the
question), and some tried to work backwards from the conclusion to be
proved, without clarifying what they were doing.
6.2:    Didn't write what arithmetic rules you were using.
Didn't simplify a number n to the smallest one congruent to it
modulo 19, and therefore had to do long computations.