Question 944247
Since those are the only three possibilities (late, early or on-time), their sum must be 1.
{{{P+3/8+5/13=1}}}
{{{P+(3/8)(13/13)+(5/13)(8/8)=104/104}}}
{{{P+39/104+40/104=104/104}}}
{{{P+79/104=104/104}}}
{{{P=25/104}}}