Question 255607
Put this into a chart:
first . . . . .X . . . . .(3/4)X . . . . .  (1/2)X . . . . (1/4)X . . . . 0X
second  . . .Y . . . .(5/6)Y . . . . . . (4/6)Y . . . .(3/6)Y . . . . (2/6)Y . . . .(1/6)Y . . . . 0Y
time . . . . .0 . . . . .1 . . . . . . . . . .2 . . . . . . . . .3 . . . . . . . .. 4 . . . . . . . 5 . . . . . . .6

Notice that 2*(1/4) = 1/2. This occurs at 3 hours.