Question 288053
The number of ways of partitioning a set of n objects into r cells with N1 elements in the first cell, N2 elements in the second, and so on until Nr is:

{{{n!/N1!N2!Nr!}}}

There are 4 tennis players, which makes 2 pairs (“cells”). Therefore, the solution would be:

{{{4/2.2=4!/2!2!}}}

4!/2!2! = 4.3.2!/2.1.2! = 12/2 = 6 possibilities (B)

<img src="http://tinypic.com/r/105t81x/5">