An XM-1 tank has a mean time between failures (MTBF) of 810 kilometers according to an exponential distribution. The document asks: (a) what is the maximum mission length for a 0.98 chance of returning, (b) the probability of returning from a 160km mission, and (c) how many tanks are needed for a 0.99 probability that at least 5 will arrive at an 80km target.