Answer :
[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]
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
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