Normal Approximation

Here is a simple probability model for multiple-choice tests. Suppose that each student has probability p of correctly answering a question chosen at random from a universe of possible questions. (A strong student has a higher p than a weak student.) Answers to different questions are independant. Jodi is a good student for whom p=0.75

a)Use the normal approximation to find the probability that Jodi scores 70% or lower on a 100-question test.
b)If the test contains 250 questions, what is the probability that jodi will score 70% or lower?