This is a question about probability, please help me out.

Question 4: A manufacturer of cell phones has 100 cell phones randomly chosen from each day's production and checked for defects. A defect rate of 10% is considered acceptable, and we can assume that 10% of all manufacturer's cell phones are actually defective: a) Algebraically show that we can use the normal approximation to the binomial distribution. b) What is the probability that between 9 and 11 cell phones are defective? c) What is the probability of finding 8 or more defective cell phones in the sample? d) What is the probability of finding less than 8 defective cell phones in the sample? Marking Scheme (out of 12) 2 marks to algebraically show that we can use the normal approximation to the binomial distribution . 2 marks to create an equation, 1 mark to simplify and 1 mark to look up the z-score and state the probability for each of b) and c) (out of 8) 2 marks for creating an equation for d), using the indirect method Show that we can use the normal approximation to the binomial distribution: P(9