Question 961974
.
You have 0.35 liters of an acid solution whose acid concentration is 15%. 
How many liters of pure water should be added to lower the concentration to 7%?
~~~~~~~~~~~~~~~~~~~~~~~~~~


        @lwsshar3 in his post gives an answer 40.
        40 of what ? Liters ?
        But this is an absurd.


        There is a rude error in calculations by @lwsshar3.
        I came to bring a correct solution.



let x=amt of pure water should be added (in liters).
0.15*0.35 = 0.07*(0.35+x)
0.0525 = 0.0245 + 0.07x
0.07x = 0.0525 - 0.0245
0.07x = 0.028
x = 0.028/0.07 = 0.4.
How many liters of pure water should be added to lower the concentration to 7%?     0.4 of a liter.


<U>CHECK</U>. &nbsp;&nbsp;&nbsp;&nbsp;The final concentration is &nbsp;&nbsp;{{{(0.35*0.15)/(0.35+0.4)}}} = 0.07, &nbsp;&nbsp;or &nbsp;&nbsp;7%. &nbsp;&nbsp;&nbsp;&nbsp;! precisely correct !


Solved correctly.


The lesson to learn: when you make calculations, keep the dimensions consistent and be accurate.