Question 133718
Let x=amount of pure water needed

Now we know that the amount of pure salt in the water (0) plus the amount of pure salt in the 5 liters (0.85*5) has to equal the amount of pure salt in the final mixture 0.68(5+x).  So our equation to solve is:

0.85*5=0.68(5+x)  simplify
4.25=3.4+0.68x  subtract 3.4 from each side
4.25-3.4=3.4-3.4+0.68x  collect like terms
0.85=0.68x  divide both sides by 0.68

x=1.25 liters---------------------------Amount of pure water needed

CK

0.85*5=0.68*6.25
4.25=4.25


Hope this helps---ptaylor