How many milliliters of a 9.0\% ({\rm v/v}) propyl alcohol solution would you need to obtain 4.0{\rm mL} of propyl alcohol

Answer 1

What's the solvent? Water?
9% v/v means 9.0 mL propyl alcohol in 100 mL solution. You want 4 mL propyl aocohol.
(9 mL/100 mL) x ? = 4 mL
? = 4*100/9 = ?