Answer:
33% off the regular price
Explanation:
Lets give these a variables to help us better understand this concept
In our scenario lets say the price is $10.00 and you get 10 milliliters prior to the special, this is arbitrary as any values would do
33% extra free
For the 33% extra free deal you get 3.3 milliliters more for $10 for a total of 13.3 milliliters [Math behind this solution: (10*.33)+10]
So now to know how much you're getting per dollar:
13.3/10 = 1.33 ml per dollar
33% off the price
This basically means 67% of the actual price so with that being said
you'd be paying $6.7 for 10 ml. This means you get 1.49 ml per dollar
Compare
1.33ml vs 1.49ml
1.33 < 1.49 so thus 33% off the price is a better deal