Question 1121249
x, time for the slower tank, alone

{{{1/x+2.5/x=1/7.5}}}


{{{3.5/x=1/7.5}}}


{{{x/3.5=7.5}}}


{{{x=(3.5)(7.5)}}}


{{{x=26.25}}}

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Rate for the fast pipe, working alone,
{{{2.5/26.25}}}


TIME for the fast pipe,
{{{26.25/2.5}}}


{{{highlight(10.5)}}} hours