Professor Smith assigns letter grades in a large class

Question 1 and 2 are based on the information below:

Professor Smith assigns letter grades in a large class using the following criteria:

Top 10% = A

Next 25% = B

Next 50% = C

Next 15% = D or F

The points are normally distributed with a mean = 500 and a standard deviation, s = 100.

1.Greg had 575 points, hence his grade would be

(a) A

(b) B

(c) C

(d) D or F

2.Joe said "A couple of more points and I would have had a C." Which of these scores could be Joe's?

(a) 395

(b) 405

(c) 445

(d) 495