Two laptop manufacturing companies A and B are fierce rivals. A's laptop have a mean life of 4.9 years with a standard deviation of 1.2 years while B's laptop have a mean life of 4 years with a S.D of 1 year. Find the probability that a random sample of 25 of A's laptop will have a mean life that is at least 1 year longer than that of a random sample of 49 of B's laptop.