Given a set of elements N={1,2,.....,n} and two arbitary subsets A and B belonging to N,

how many permutations Pi from N to N satisfy min(pi(A))=min(pi(B)), Where min(S) is the smallest integer in the

set of integers S, and pi(S) is the set of integers obtained by applying permutation pi to

each element of S?

It has been over a decade since I dealt with math problems on a daily basis. What level of math is this anyway? I only needed two advanced calculas classes to get a degree in mathematics. I admitted forgot most of what I learned shortly after graduation.

this kind of mathematics is called Discrete mathematics and I guess it should be a little above Graduation

Ok i doubt about the question,I think it is incomplete

Lets take a situation where a set is {1,2,3,4,5}

of which let us take set a as a={1,2,3} and let us take set b as b={3,4,5}

then according to question

atleast one combination should be there such that a=b ie (a{123}=b{345}) like this.

So it is possible only when some common elements exist with in subsets.

yup so the answer must contain the term (A^B) where ^ is intersection