Question 961638
Let {{{ t }}} = time in hours
{{{ 1/t }}} = the experienced plumber's
rate of working
{{{ 1/(2t) }}} = the apprentice's rate of working
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Add their rates to get their rate
working together
{{{ 1/t + 1/(2t) = 1/5 }}}
Multiply both sides by {{{ 10t }}}
{{{ 10 + 5 = 2t }}}
{{{ 2t = 15 }}}
{{{ t = 7.5 }}}
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The apprentice, working alone, takes 15 hrs
check:
{{{ 1/t + 1/(2t) = 1/5 }}}
{{{ 1/7.5 + 1/15 = 1/5 }}}
{{{ 2/15 + 1/15 = 3/15 }}}
{{{ 3/15 = 3/15 }}}
OK