Question

A brown flask contains a concoction that is 20% alcohol. A red flask contains a concoction with an unknown amount of alcohol. An equal amount of both flasks is poured into an empty jug. If the resulting mixture has an alcohol concentration that is 30% greater than the alcohol concentration of the brown flask, what percent alcohol did the red flask originally contain?

Answer 1

Let us say the the red flask contained the concoction with x % of alcohol.

Let 1 liter from each flask be mixed. The total amount of alcohol in the mixture is:  200 ml + 10 * x ml.  Total volume of mixture = 2, 000 ml

So % of alcohol in the mixture
    (200 + 10x)/2000  = 20% + 30%
    20 + x = 2 * 50 = 100
 x = 80

The percentage of alcohol in red flask = 80%