Question

Given a random permutation of the elements of the set {a,b,c,d,e}, let X equal the number...

Given a random permutation of the elements of the set {a,b,c,d,e}, let X equal the number of elements that are in their original position (as listed). The moment generating function is X is: M(t) = 44/120 + 45/120e^t + 20/120e^2t + 10/120e^3t+1/120e^5t Explain Why there is not (e^4t) term in the moment generating function of X ?

Homework Answers

Answer #1

Since there are exactly 5 terms which needs to be arranged. If we want to put exactly 4 out of 5 numbers in their original place, it is not at all possible. Because if 4 are at their original place, the 5th one will automatically goes it it's original place. It simply means we can't de arrange the position of exactly 1 of 5 number because to do that, we need any other place. So we can't keep exactly 4 out of 5 numbers in its original position. That's why it's probability is 0. So, there is no terms of e4t in the moment generating function of X.

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