Question 924087
In {{{ 15 }}} days, they will finish {{{ 15/25 = 3/5 }}} of the room
There is {{{ 2/5 }}} of the room left to build
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After Y goes away, X's rate of working is:
{{{ (2/5) / 20 }}} rooms / days
{{{ (2/5) / 20 = 1/50 }}}
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Plug this result into equation for working together:
Let Y's rate of working = {{{ 1/d }}} rooms/days
{{{ 1/50 + 1/d = 1/25 }}}
{{{ 1/d = 2/50 - 1/50 }}}
{{{ 1/d = 1/50 }}}
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Working separately, X and Y both
work at the rate of ( 1 room ) / ( 50 days )