Jack mows the lawn in 3 hours. Jane mows the same yard in 4 hours. If they worked together how much time would it take them to mow the yard?

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

[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]