Question 1099284
Work rate can be in the unit of GARDENS per MINUTES, and then the combined rate for John and Jack working together is the sum of their rates.


JOHN,  {{{(1/30)(gardens/minute)}}}

JACK,  {{{(1/20)(gardens/minute)}}}


John and Jack together on the same job:
{{{1/30+1/20}}}


{{{2/60+3/60}}}


{{{5/60}}}


{{{reduce_the_fraction}}}


{{{1/12}}}---------------------1 garden in 12 minutes;  or TWELVE MINUTES to dig ONE GARDEN