Solution A is made up of alcohol and water mixed in the ratio of

25 units of A contain 21 units of alcohol and 4 units of water. So, 5 units of A contain (21/5) units of alcohol and (4/5) units of water
5 units of B contain 2 units of alcohol and 3 units of water

If we mix 5*5=25 units of A with 5*6=30 units of B (so that A and B are mixed in the ratio of 5:6), the resultant 55 units solution will contain:
Alcohol: (21/5)*5 + 2*6 = 33 units
Water: (4/5)*5 + 3*6 = 22 units

% of alcohol in the resultant solution = (33/55)*100 = 60

ANS: C

Solution A is made up of alcohol and water mixed in the ratio of 21:4 by volume; Solution B is made up of alcohol and water mixed in the ratio of 2:3 by volume. If Solution A and Solution B are mixed in the ratio of 5:6 by volume, what percent of the resultant mixture is alcohol?

Solution:

____________Alcohol____Water____Total
Solution A___21_________4_________25
Solution B___2__________3__________5

Convert to %
(%)__________Alcohol____Water______Total
Solution A___84%_________16%______100% (X by 4 to get %)
Solution B____40%________60%______100% (X by 20 to get %)

Wt. avg. option 1:
40%___________________________84%

sol. A to sol. B is 5:6 (total 11) dividing line between 40% and 84% into 11 segments,(44%/11) 4% per segment.

(sol. B) 40%______5________x_____6________84% (sol. A)

We have 5 segments distance from x, so 6 * 4% each segment = 24%
24% lower than 84%, which is 60%

Wt. avg. option 2:

6/5 = (84%-w)/(w-40%)

w =60%

answer: C 60%

solution A ratio is 21:4 ..so for every 25ml, 21 ml alcohol
solution B ratio is 2:3 ..so for every 25ml, 10 ml alcohol

let 25*5 ml of A and 25*6 ml of B be mixed. total alcohol volume is (21*5)+(10*6) = 165. mixture volume is 275. so 165/275 * 100 is 60%. thus answer is C