A chemist needs to make 30 ounces of a 30 % alcohol solution by mixing a 15% alcohol solution with a 40 % alcohol solution

alcohol-solution

#1

A chemist needs to make 30 ounces of a 30 % alcohol solution by mixing a 15% alcohol solution with a 40 % alcohol solution

How many ounces of the 40% solution does she need?

Answer:

18 oz. of the 40% solution, 12 of the 15%

let a and b represent the quantities in ounces of 15% and 40% alcohol solution respectively.
according to the given conditions
a+b =30…1
0.15a+0.4b =0.3*30 =9…2

multiply eq 1 by 0.15
0.15a +0.15b = 30*0.15 =4.5…3
subtract eq 3 from eq 2
0.25b = 4.5
b=18
18 ounces of 40 % soln is needed.