Question 71090
Call the time it takes to fill the 2nd tank x hrs
Rate of filling 1st tank + rate of filling 2nd tank = combined rate of filling
1 tank / 4 hrs + 1 tank / x hrs = 1 / (x-2) hrs
{{{1/4 + 1/x = 1/(x-2)}}}
{{{x(x-2) + 4(x-2) = 4x}}}
{{{x^2 - 2x + 4x -8 = 4x}}}
{{{x^2 - 2x -8 = 0}}}
{{{x - 4)(x + 2) = 0}}}
x = 4 hrs answer
check
{{{1/4 + 1/x = 1/(x-2)}}}
{{{1/4 + 1/4 = 1/2}}}
{{{1/2 = 1/2}}}
OK