Question 1155447
Just looking at the concentration values, see one part out of six parts from 50% to 80%; the wanted 55% is one part.  You want most of the alcohol solution to come from the 50% and the rest from the 80%.  Think  270*(5/6)=225 mL from the 50% and 45 mL from the 80%.



v, amount of the 80%
270-v, amount of the 50%
55, the target concentration percent wanted


{{{80v+50(270-v)=55*270}}}

after doing the algebra steps,


{{{highlight(v=270((55-50)/(80-50)))}}}-------volume of the 80% alcohol to use.