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Gilbert can do a job in 30 mins, harry can do it 40 mins., and irish can do it in 60 mins. how long will it take them finish the job if they work together?

Sagot :

t/30 + t/40 + t/60 =1
*get the LCD which is 120
4t + 3t + 2t = 120
9t= 120
t = 120/9 or 40/3 mins