Question

In 91% (by volume) isopropyl alcohol (a large [compared to water], flammable molecule) solution, there are only two substances: the alcohol, and water. So when I poured 50 mL of 91% isopropyl alcohol into a graduated cylinder, how many milliliters were alcohol? How many were water? I’ll answer the first questions, putting a line through units that cancel. Then you answer the following questions doing the same.
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(91ml(iso) / 100ml(sol)) x 50ml(sol) = 45.5ml(iso) (because ml(sol) / ml(sol) =1, right?)

50 ml(sol) – 45.5ml(iso) = 4.5ml(water)

So, when I added 50 ml of water to the 91% isopropyl alcohol solution, how many total milliliters of water were in the solution?