re: HSC Physics Marathon Archive
For person A, it would take 25/0.8 = 31.25 years
For person B, it would take 25/0.6 = 41.67 years
But time also dilates so...
using tv = t0 / √(1-v^2/c^2)
For A, 31.25√ (1-(0.8)^2 = 18.75 years
For B, 41.67√ (1-(0.6)^2 = 33 years
So B will be older...