Question 732697
Add the rate of pumping
{{{ 1/1 + 1/4 = 1/t }}}
{{{ 4t + t = 4 }}}
{{{ 5t = 4 }}}
{{{ t = 4/5 }}}
{{{ (4/5)*60 = 48 }}}
It will take 48 min using both pumps
check:
{{{ 1/1 + 1/4 = 1/(4/5) }}}
{{{ 4/4 + 1/4 = 5/4 }}}
{{{ 5/4 = 5/4 }}}
OK