Cross Training-Elementary Algebra?

Try and think about it as a number of stairs (n). The time for the first bit of the workout (the way up) is n*(1/2). the time for the second bit of the workout is n*(1/3) add those two times together and we get (5/6)n=90 seconds this tells you that there are 108 stairs. so it takes him 54 seconds to ascend.