Question 155003

Let x=amount of 70% rubbing alcohol needed
Then 3.5-x=amount of water needed

Now we know that the amount of pure alcohol in the 70% solution (0.70x) plus the amount of pure alcohol in the water (0) has to equal the amount of pure alcohol in the final mixture (3.5*0.45).  So our equation to solve is:

0.70x=3.5*0.45 or
0.70x=1.575  divide each side by 0.70
x=2.25 ounces-----------------------------amount of 70% alcohol needed
3.5-x=3.5-2.25=1.25 ounces---------------- amount of water needed

CK

2.25*0.70=3.5*0.45
1.575=1.575

Hope this helps---ptaylor