/sci/ - Science & Math

VJack = 1 room / 3 hours = 1/3 rooms per hour
VJohn = 1 room / 2 hours = 1/2 rooms per hour

VJack + VJohn = 1/3 + 1/2 = 5/6 rooms per hour

T(Jack + John) = 1 room / (5/6 rooms per hour)
= 6/5 hours.