How to select randomly from a matrix?

Dear all,

I got one problem here and hoping someone can help me on this. Say I have a
50 by 2 matrix and I don't know how to randomly select:

1. a pair of observations from the last 10th of the 50 observation from the
matrix.
2. how to select randomly an observation from the first 5 observations of
the second column in the matrix?

Thanks....hope to hear from someone soon

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