Total = 36oz Amount of 18% solution = x Amount of 9% solution = 36 - x
Using the fact that (amount of solution) * (percent HCl) = amount HCl we can set up an expression for the amount HCl in a mixture of 18% and 9% solutions with a total volume of 36oz.
Amount of HCl = x*0.18 + (36 - x)*0.09
If we divide this by the amount of solution we get percent HCl, and we have a target of 10% HCl. Now we have an equation to solve,
[x*0.18 + (36 - x)*0.09]/36 = 0.1
x*0.09 + 3.24 = 3.6
.09x = 0.36 x = 4
Therefore, 4 ounces of 18% HCl solution and 32 ounces of 9% HCl solution
To find how many minutes of talk time is available per dolla, you have to divide 160 (number of minutes) by 40 (cost)
160/40 = 4
Therefore, it's 4 minutes per dollar
