PISA is an international survey conducted every three years among school students in a number of countries. The survey in 2009 included 4,700 students from Norway. In the natural sciences, the Norwegian students scored an average of 500 points. It was exactly like the international average. The standard deviation for Norwegian pupils was 80 points. We randomly pull out a student among the Norwegian participants. You can expect the student's score to be normally distributed.

a) Determine the probability that the student scored at least 650 points.
b) Determine the probability that the student scored between 475 and 535 points.