Question 370440
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Hi,
Let x represent the time second tank would take alone.  
then the time the first tank to fill alone would be(x+3)
***Two pipes can fill a tank in two hours.  Per hour is the equalizer.
1/x + 1/(x+3) = 1/2hr
Mulitplying each term on both sides of the equation by 2x(x+3) so as all denominaotrs = 1
2(x+3) + 2x = x(x+3)
solving for x
2x + 6 + 2x = x^2 + 3x
x^2 -x -6 = 0
factoring
(x-3)(x+1)= 0
(x-3)=0  x = 3, 
(x+1)= 0 x = -1  (cannot use)
3hr = time second tank would take alone, first tank 6hr alone
checking our answer
1/6 + 1/3 = 1/6 + 2/6 = 3/6 = 1/2