Question 524430
Add their individual rates of working to get
their rate working together
In words:
( 1 driveway/Derek's time ) + ( 1 driveway / Ken's time ) = ( 1 driveway/time working together )
Let {{{t}}} = Ken's time to shovel driveway alone
given:
Derek's rate = {{{ 1/50 }}} 
Rate working together = {{{ 1/30 }}}
----------------------------
{{{ 1/50 + 1/t = 1/30 }}}
Multiply both sides by {{{ 150t }}}
{{{ 3t + 150 = 5t }}}
{{{ 2t = 150 }}}
{{{ t = 75 }}}
It will take Ken 75 minutes, or 1 hour and 15 min
to shovel the driveway by himself