among others, problems 5,10, and 14.b are very good.

in problem 4, the sum of the points is not 25.
perhaps problem 4.c is worth 5 points.

problem 13 (polluted water problem).
 the text should specify that the events corresponding to errors
 in repeated executions of the test are mutually independent.
 btw this is somewhat irrealistic. perhaps the idea is that
 students have to figure out by themselves the issue of independence
 and discuss it in their answer?