Let A=\1,2,3, , 7\ and let P(A) denote the power set of A. If the number of functions f: A P(A) such that a f(a), a A is mn, m and n N and m is least, then m+n is equal to .
Answer
44
Solution
f(a) = a subset of A that contains a
f(a)=\a\ (any subset of the other 6 elements)
26 choices for each f(a), independently for all 7 elements
number of functions = (26 )7=242=mn
m is least m=2, n=42
m+n=44
Answer: 44