let the numbers be x and y
x+y=27.........[1]
one half of the first number plus one third of the second number is 11
1/2x+1/3y=11
(3x+2y)/6=11
3x+2y=66........[2]
x+y=27
multiply by 2
2x+2y=54.......[1]
3x+2y=66.......[2]
subtracting eqn 2 from 1 we get
2x+2y=54
3x+2y=66
-x=-12
x=12
y=27-x=27-12=15
Hence the numbers are:
12,15