Answer :

konrad509
[tex]\frac{1}{3}+\frac{1}{4}=\frac{1}{x}\\ \frac{4}{12}+\frac{3}{12}=\frac{1}{x}\\ \frac{7}{12}=\frac{1}{x}\\ 7x=12\\ x=\frac{12}{7}\hbox { h}=1\hbox{ h }42\hbox{ min } 51.43 \hbox{ s} [/tex]
AL2006
Jack mows 1/3 of the lawn each hour.
Jane mows 1/4 of the lawn each hour.

Working together, they mow (1/3 + 1/4) of the lawn each hour.

In order to add the fractions, you need a common denominator.
12 will work:

(1/3 lawn/hour + 1/4 lawn/hour) = (4/12 + 3/12) = 7/12 lawn/hour.

This rate of work produces 12/7 hour/lawn.

12/7 hour = 1 hour    42 minutes    51.4 seconds

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