Question 636083
1/4 + 1/6 = 1/t


(1/4)(3/3) + (1/6)(2/2) = 1/t


(1*3)/(4*3) + (1*2)/(6*2) = 1/t


3/12 + 2/12 = 1/t


(3+2)/12 = 1/t


5/12 = 1/t


5t = 12*1


5t = 12


t = 12/5


t = 2  2/5


So it will take 2  2/5 hours, or 2.4 hours (which is 2 hours, 24 minutes) for them to do it together.