Question 1196109
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Tutor @ikleyn has shown one good way to solve the problem mentally, using logical reasoning and simple arithmetic, without algebra and equations.<br>
Here is a different such path to the answer.<br>
Since the head gardener works twice as fast as his assistant, when working together he does 2/3 of the job.<br>
So in the 4/3 hours it takes them to do the job together, the head gardener does 2/3 of the job; that means the number of hours it would take him to do the job alone is (3/2)(4/3) = 2.<br>
ANSWER: 2 hours.<br>