<PRE><B>Question 1200677</B>
&lt;br&gt;
We can ignore the fact that a salt concentration of 72% is not possible and treat the problem as a mathematical exercise.&lt;br&gt;
A couple of the other tutors have done that and shown algebraic solution methods.  Here is a different method.&lt;br&gt;
The increase of 8% in the concentration makes the new concentration 80%.  So 72% of the original 180 L is equal to 80% of the new total volume.&lt;br&gt;
Let x be the new volume; then&lt;br&gt;
{{{.72(180)=.80(x)}}}&lt;br&gt;
{{{x=(.72(180))/.80=(9/10)(180)=9*18=162}}}&lt;br&gt;
So the amount of water that must be evaporated is 180-162 = 18 L.&lt;br&gt;
ANSWER: 18 L&lt;br&gt;
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