It belongs to Statistics. Please explain with definition

3. All printed circuit boards (I'CBs) that are manufactured at a certain plant are inspected. An analysis of the company's records indicates that 20% of all PCBs are flawed in some way. Of those that are flawed, 80% are reparable and the rest must be discarded. If a newly produced PCB is randomly selected. what is the probability that it does not have to be discarded? (10 points) 4. Hits on a personal website occur quite infrequently. They occur randomly and independently with an average of ten per week. Find the probability that the site gets 10 hits in a week. (10 points) (Hint: Use Distribution) 5. In answering a question on a multiple choice test a student either knows the answer or he guesses. Let p=0.6 be the probability that she knows the answer and 1-p=0.4 the probability that she guesses. Assume that a student who guesses at the answer will be correct with probability 1/m, where m=5 is the number of multiple-choice alternatives. What is the conditional probability that a student knew the answer to a question given that she answered it correctly? (10 points) 6. The Ajou catalog department that receives the majority of its orders by telephone conducted a study to determine how long customers were willing to wait on hold before ordering a product. The length of time was found to be a random variable best approximated by an exponential distribution with a mean equal to 3 minutes. What is the value of 2, the parameter of the exponential distribution in this situation? (5 points) What proportion of customers having to hold more than 1.5 minutes will hang up before placing a rder? (5 points) Find the time at which 50% of the customers will continue to hold? (5 points)