College Algebra
posted by Liz on .
How many liters of 80% hydrochloric acid must be mixed with 40% hydrochloric acid to get 15 liters of 65% hydrochloric acid? Write your answer rounded to three decimals. Show all work.

Work with the total volume of HCl
The amount of HCl in a liters of 80% acid is just .8a
In b liters of 40% acid is .4b
Total acid: .65*15
Total volume: a+b
.8a + .4b = 9.75
a + b = 15
.8a + .4b = 9.75
.8a +.8b = 12
.4b = 2.25
b = 5.625 liters of 40% acid
a = 9.375 liters of 80% acid 
9.375

how much acid is in 50 liters of 80% solution