15 litres of mixture contains 20% alcohol and rest of water. if 3 litres of water be mixed with it the percentage of alcohol in the new mixture would be

50/3

total mixture is 15 liters
out of which 20% is alcohol so total alcohol is=
20% of 15 liters= 20*15/100=3 liters

the rest is water,so water content= 12 liters

on adding 3 more liters of water,
the total water will be 15 liters and the alcohol will still be 3 liters.so the total mixture would be 18 liters.

so the alcohol percentage in new mixture
=3 liters out of 18
=3*100/18
=16.67%

16.67