Question 1196109
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The head gardener can mow the lawns in the city park twice as fast as his assistant. 
Working together, they can complete the job in 1 1/3 hours.
How long would it take the head gardener working alone?
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According to the problem, the head gardener works as productive as two his assistants.


So, the problem statement is equivalent as if to say that three assistants will complete the job in 1 1/3 hours, 
or in 60 + 20 = 80 minutes, working together.


Hence, one assistant will complete the job in 80*3 = 240 minutes.


For the head gardener, it will take only half of this time, i.e. 240/2 = 120 minutes,
or 2 (two) hours.    


<U>ANSWER</U>.  The head gardener will complete the job in 2 hours, working alone.
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Solved MENTALLY, using reasoning and without using equations.