Question 999272
The current problem works this way:
Bob's rate, {{{1/3}}}.
Al's rate, {{{1/4}}}.
Both together,  {{{1/3+1/4=4/12+3/12=highlight(7/12)}}}.  The unit is LAWNS per HOUR.
....Yes, you can look at that rate upside down to figure how much TIME for one job and this is  {{{12/7}}}  HOURS per job.  Twelve hours for seven jobs or, {{{1&5/7}}}  hours for one job or however you want to express it.





The "previous" problem works this way:
Al works {{{1&1/2}}} hours, and does some work; and then Al and Bob work together for some unknown {{{t}}} hours and they finish the 1 job.
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{{{highlight_green((1/4)(3/2)+(7/12)*t=1)}}}.
Solve this for t.