A farmer uses a machine to dispense insecticide from large plastic barrels. One-fifth of the insecticide in a barrel has been dispensed. If the remaining insecticide is dispensed at a rate of 1/10 of a barrel per minute, how long will it take for the barrel to be empty
If one-fifth of the insecticide in the barrel has been dispensed, then there is 1 - 1/5 = <<1-1/5=4/5>>4/5 of the insecticide remaining.
The rate at which the remaining insecticide is being dispensed is 1/10 of a barrel per minute.
Therefore, it will take 4/5 / (1/10) = (4/5) x (10/1) = 8 minutes to empty the barrel. Answer: \boxed{8}.