Question 511623
Let {{{t}}} = the time for them
to mow 1 lawn working together
Jack's rate of mowing:
( 1 lawn ) / ( 5 hours )
Maria's rate:
{ 1 lawn ) / ( 3 hours )
Add their rates of working:
{{{ 1/5 + 1/3 = 1/t }}}
Multiply both sides by {{{ 13t }}}
{{{ 3t + 5t = 15 }}}
{{{ 8t = 15 }}}
{{{ t = 15/8 }}} 
This is 1 hour + 7/8 of an hour
{{{ (7/8)*60 = 52.5 }}}
It takes them 1 hr and 52.5 min