2.8 percent alcohol
Because the concentration of alcohol is lower; you pay the alcohol not the water.
There is no way to calculate that with the information provided. We need to know the volume of each.
Add 5% water
The Hair of the Dog Dave has the highest alcohol content which is 29% ABV.
2/3 of 70% and 1/3 of 10%
The highest level spirit it is possible to brew at all is only around 96.5%. At this point the water-alcohol solution becomes azeotropic, meaning that distillation can't separate them further.
A bottle will usually state it's alcohol by volume (ABV) as "proof" . Proof is double what the percentage of alcohol is. So, a bottle of 60 proof spirits would be 30% alcohol by volume. The highest percentage alcohol in a spirit that I've seen is 151 proof, and that was a bottle of rum.
4 ounces
You mix the pure alcohol with something else, for example, water.
Pure alcohol is far more dangerous than adulterated alcohol because pure alcohol has one hundred percent alcohol in comparison to aldulterated alcohol which is less than 100 percent.
50% alcohol Proof ÷ 2 = % alcohol