Question 377620
Hi
the larger one can fill the tank in 18hrs less than the smaller one.
Let x represent the time for the smaller alone, 
then (x-18hr)would be the time for the larger alone
Per hour is the Equalizer
1/x + 1/(x-18) = 1/12 Mulitiplying each term by 12x(x-18)so all denominators = 1
12(x-18) + 12x = x(x-18)
solving for x
12x - 12*18 +12x = x^2 - 18x
24x - 12*18 = x^2 - 18x
x^2 - 42x + 216 = 0
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
{{{x = (42 +- sqrt( 900))/(2) }}}
x = 6  Cannot use
x = 36hr, the time for the smaller alone.  18hr for the larger alone (36-18)
CHECKING our Anwer
1/36 + 1/18 = 2/72 + 4/72 = 6/72 = 1/12