Three computers can print out a task in 10 min, 15 min, and 30 min, respectively. How long would it take to complete the task with all three computers working?

Answer 1

computers do 1/10, 1/15 and 1/30 of task in one minute

collectively do 3/30 + 2/30 + 1/30 = 1/5 of task in one minute

so together would do whole task in 5 minutes