Question 1033124
.
A certain quantity was taken from a ten liter 30% alcohol solution and replaced by pure alcohol so as 
to produce 51% alcohol solution. How many liters were taken and replaced?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


<pre>
Let "x" be the volume of the 30% alcohol solution taken from and replaced.

After replacement, we have the same volume of 10 liters of the (new) solution.
The alcohol content in the new solution is x + 0.3*(10-x).

Since it is 10 liter of the 51% of alcohol solution, you have this equation

x + 0.3*(10-x) = 0.51*10.

Simplify and solve for x:

x + 3 - 0.3x = 5.1,

0.7x = 5.1 - 3,

0.7x = 2.1,

x = {{{2.1/0.7}}} = 3.

<U>Answer</U>.  3 liters of the original solution were taken off and replaced by the pure alcohol.
</pre>