Question 1140225
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<pre>
Considering rate of work of separate pumps and their combined rate, you get this basic equation


{{{1/x}}} + {{{1/(x+7)}}} = {{{1/12}}},


where x is the time for the larger (=for the faster) pump.


Solve it for x, which is the value under the question.


The solution is reducing the problem to a quadratic equation.


The way to do it is to multiply both sides of the given equation by 12x*(x+7).
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