Two functional verification servers, A and B, are processing a massive test regression suite. Server A working alone takes 12 hours to finish the suite. Server B working alone takes 24 hours. They start processing the suite together at the same time. However, after 4 hours, Server A crashes. How many additional hours will it take Server B, working alone, to finish the remaining tests in the suite?
Server A completes 1/12 of the suite per hour. Server B completes 1/24 per hour. Working together, their combined rate is (1/12 + 1/24) = (2/24 + 1/24) = 3/24 = 1/8 of the suite per hour. After 4 hours together, they have completed 4 * (1/8) = 4/8 = 1/2 (half) of the suite. Server B must complete the remaining 1/2 alone. Since Server B takes 24 hours for a full suite, it will take 12 hours to complete a half suite.
