11154번 - Birthday Party 스페셜 저지다국어

N persons have been invited to a somewhat special birthday party. Each person brings one present, but the recipent of each present is determined randomly. A person never receives his own present, but all other persons are equally likely recipients. What is the probability that one can find k persons at the party such that person 1 gives his present to person 2, person 2 gives his present to person 3 and so on to person k which gives his present to person 1?

The first line of the input consists of a single integer T, the number of test cases. Each test case consists of two integers N and k.

• 0 < T ≤ 30
• 2 ≤ N ≤ 10000000
• 2 ≤ k ≤ N

For each test case, output the probability with an accuracy of at least 10⁻⁶.