SOLUTION: how many litres of a solution containing 18% sulphuric acid by volume, and how many litres of another solution containing 25% sulphuric acid must be combined to make 550 L of solut

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Question 1127833: how many litres of a solution containing 18% sulphuric acid by volume, and how many litres of another solution containing 25% sulphuric acid must be combined to make 550 L of solution containing 23% sulphuric acid?
Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


Algebraically, solve the equation that says x liters of .18 solution plus (550-x) liters of .25 solution yields 550 liters of .23 solution:

0.18%28x%29%2B0.25%28550-x%29+=+0.23%28550%29

I'll let you do the algebra to finish.

But here is a method for finding the answer that, if you understand it, will get you to the answer to a problem like this much faster and with much less work.

Think of starting with the 18% solution and adding some 25% solution, stopping when the mixture is 23%. The 23% is 5/7 of the way from 18% to 25%; that means 5/7 of the mixture needs to be the 25% solution.

%285%2F7%29%28550%29+=+2750%2F7; %282%2F7%29%28550%29+=+1100%2F7

The mixture needs to have 2750/5 liters of 25% solution and 1100/7 liters of 18% solution.