Question 688446
1/12 + 1/t = 1/3


t/(12t) + 12/(12t) = 1/3


(t + 12)/(12t) = 1/3


3(t + 12) = 12t


3t + 36 = 12t


36 = 12t - 3t


36 = 9t


t = 36/9


t = 4


So if the second pump is only used, it will take 4 minutes.