Question 709181
Add their rates of working to get rate 
working together
Amy's rate is ( 1 house ) / (  9 hrs )
Let {{{ 1/t }}} = Tom's rate
Their rate working together is {{{ 1/5 }}}
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given:
{{{ 1/9 + 1/t = 1/5 }}}
Multiply both sides by {{{ 45t }}}
{{{ 5t + 45 = 9t }}}
{{{ 4t = 45 }}}
{{{ t = 13.75 }}}
It will take Tom 13 hrs and 45 min working alone
check:
{{{ 1/9 + 1/t = 1/5 }}}
{{{ 1/9 + 1/13.5 = 1/5 }}}
You can check with calculator