I have a relatively simple problem that I'm having trouble with. A ship is going at 0.90 c, over a distance of 80 light years. In my text the method for determining the time spent traveling is: 80 years + (0.1 * 80) = 88 years This method seems logical, at 0.9 of the speed of light this trip should take 80 years plus that missing 0.1 of the speed of light. I tried t = d/v : t = 80 years / (0.9 light years per year) t = 88.888889 I'm not sure what is going on, I see no logical error with either approach. Any help is appreciated.