Answer:
18.02
Step-by-step explanation:
We have the following formula of dilutions in chemistry.
C1 * M1 = C2 * M2
We have a 64 ounce bottle of 91% alcohol. Therefore C1 91% and M1 64, and to decrease to 71% that is C2.
solving for M2
M2 = C1 * M1 / C2
Replacing
M2 = 91% * 64/71%
M2 = 82.02
M2 is the total, so you must add
82.02 - 64 = 18.02
