A mission-critical production system has n stages that have to be performed sequentially; stage i is performed by machine Mi . Each machine Mi has a probability ri of functioning reliably and a probability 1 − ri of failing (and the failures are independent). Therefore, if we implement each stage with a single machine, the probability that the whole system works is r1 · r2 · · · rn. To improve this probability we add redundancy by having mi copies of the machine Mi that performs stage i. The probability that all mi copies fail simultaneously is only (1−ri) mi , so the probability that stage i is completed correctly is 1−(1−ri) mi and the probability that the whole system works is Πn i=1[1 − (1 − ri) mi ]. Each machine Mi has a cost ci , and there is a total budget B to buy machines. (Assume that B and the ci are positive integers.) Given the probabilities r1,...,rn, the costs c1,...,cn, and the budget B, find the redundancies m1,...,mn that are within the available budget and that maximize the probability that the system works correctly.

i believe the answer would be b. within an intersection or on a crosswalk. hope this ! : )

a  social news website  is an  internet  website  that features  user-posted stories. such stories are ranked based on popularity, as voted on by other users of the site or by website administrators. users typically comment online on the news posts and these comments may also be ranked in popularity. since their emergence with the birth of  web 2.0, social news sites have been used to link many types of information, including news, humor, support, and discussion. all such websites allow the users to submit content and each site differs in how the content is moderated. on the  slashdot  and  fark  websites,  administrators  decide which articles are selected for the front page. on  reddit  and  digg, the articles that get the most votes from the community of users will make it to the front page. many social news websites also feature an online comment system, where users discuss the issues raised in an article. some of these sites have also applied their voting system to the comments, so that the most popular comments are displayed first. some social news websites also have a  social networking  function, in that users can set up a user profile and follow other users' online activity on the website.