Question 473257
Rate of first copier: 1/12 of a dissertation per minute


Rate of second copier: 1/8 of a dissertation per minute



Combined rate: 1/12+1/8 = 5/24 of a dissertation per minute




Now use the formula:   Rate*Time = 1, where 1 refers to ONE job completed



Rate*Time = 1


(5/24)*t = 1


5t = 24


t = 24/5


t = 4  4/5



So it will take 4  4/5 minutes, which is about 4 minutes and 48 seconds, if they work together.