Question 446856
{{{10(1/x + 1/x) + 20/x = 1}}}
==> {{{10*(2/x) + 20/x = 1}}}
==> {{{20/x + 20/x = 1}}}
==> {{{40/x = 1}}}
==> x = 40 hours, the time it would take either one of them to finish the job alone.