Question 1

What is the difference between nPr and nCr in one sentence?

Accepted Answer

nPr counts ordered selections, nCr counts unordered ones, and nPr = nCr × r!.

Question 2

What is nC0 or nCn?

Accepted Answer

Both equal 1: there is exactly one way to choose nothing and one way to choose everything.

Question 3

How many 5-card poker hands are there?

Accepted Answer

A hand is unordered, so it is 52C5 = 2,598,960.

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