Acomputer undergoes downtime if a certain critical component fails. this component is known to fail at an average rate of once per four weeks. no significant downtime occurs if replacement components are on hand because repair can be made rapidly. there are two replacement components on hand, and ordered replacements are not due for six weeks. (a) what is the probability of significant downtime occurring before the ordered components arrive? (b) if the shipment is delayed two weeks, what is the probability of significant downtime occurring before the shipment arrives?