Statistics Tutorials: What are Rare Events? When do we Consider and Event to be Unusual?

How to Write it Mathematically?

$\Pr \left( A \right)<0.05$

What Complications Can I Find?

Example

$\Pr \left( X = 6 \right)={{C}_{6, 6} \times {0.5}^{6}}\times {{\left( 1-{0.5} \right)}^{6-6}}=1\times {0.5}^{6}\times {0.5}^{0}= 0.0156$