hi could i have some help with these questions, not sure if I'm doing them right

Question 1 (10 marks) (a) Determine whether each of the following random variables has a binomial distribution. If it does, identify the values of the parameters 1% and p. (i) Let X be the number of multiple-choice questions a student gets right on a 40-question test, when each question has four choices, only one of which is correct, and the student is completely guessing. (ii) Let X be a random variable dened in the context of part (i), but 20 questions in the test have four choices and the other 20 have three choices. (iii) Let X be the total weight of 15 randomly selected apples. (b) Ten percent of all mobile phones of a certain brand are submitted for service while under warranty. Of these, 80% can be repaired, whereas the other 20% must be replaced with new units. If a company purchases 30 of these mobile phones, what is the probability that exactly three will end up being replaced under warranty