Let M = 10x+y (where x is tens digit and y is units digit)
N = 10y+x
M+N=10x+y+10y+x = 11(x+y)
This means that the sum would be divisible by 11.
We have been asked, which of the given option cannot be possible. So its 181 only, as all other nos are divisible by 11.
ISB 2011-12 thread | Ask ISB Alumni @ ThinkISB
All information related to Indian candidates and B-schools | Indian B-schools accepting GMAT scores
Self evaluation for Why MBA?