A train is moving to the right at v=.5c. Someone standing on the train throws a baseball forward (to the right) at u'=.99c (relative to him). Relative to somone on the ground, the ball appears to be traveling at a speed u which is slightly faster than .99c, but still less than c. What if the guy on the train throws the ball backwards (u'=-.99c)? Now what speed does the guy on the ground see? Try to get the approximate answer without looking at the velocity addition formula.