Question 918999
There is {{{ 1 - 4/5 = 1/5 }}} of the tub left to fill
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The rate of filling stays the same, so
rate = {{{ (( 4/5 )) / 3 }}} 
and, also
rate = {{{ (( 1/5)) / t }}}
so, I can say:
{{{ ((4/5))/3 = ((1/5))/t }}}
{{{ (4/5)*t = (1/5)*3 }}}
{{{ 4t = 3 }}}
{{{ t = 3/4 }}}
It takes 3/4 of a minute to fill the rest
check:
I can now say that the rate is:
{{{ (( 4/5 + 1/5 )) / (( 3 + 3/4 )) = (( 4/5 )) / 3 }}}
This is just ( rate ) = ( rate )
{{{ 1 / (( 15/4 )) = 4/15 }}}
{{{ 4/15 = 4/15 }}}
OK